I've been running Original Dungeons & Dragons at my awesome local game store (Unique Gifts & Games) for a few months now. I was lucky enough to get some great advice from Jeff Rients a while back, and applied most of the things he suggested. I think the game has been a great success, so I just wanted to share a few things I did and how it's all worked out.
Of course, it goes without saying that this is purely anecdotal. This is just my experience, and is not to be treated as THE ONE WAY TO RULE THEM ALL.
Setting the Game Up, Scheduling, etc.
First, I figured out what days I could run a game consistently, and how often. Wife approval is important here. I told my wife up front, "Hey, I'd really like to run this game every other week. It's important that I am considered unavailable during these times, because yes, it's only a game, but it's also a number of busy people adjusting their schedules so they can play in it. Are you cool with that?"
It's also important to be realistic about your availability. If you schedule a weekly game, but end up not being able to make it every few weeks, that's bad for everyone involved. Choose a schedule you can consistently follow through with. You can have a successful game with flaky players. Not so much with a flaky DM.
Once I got that part squared away, I contacted the game store letting them know I wanted to try to start an OD&D game that would be every other week. I told them I could do Mondays, Wednesdays, or Fridays, included a proposed start date, and asked which was best for them. Turns out Mondays were pretty slow and had table space available, and they had no issues with me running a long out of print game. I hear some stores take issue with running games they don't sell, but I guess I just lucked out in this regard.
Once game dates, times, an so forth are set, you have to get players there.
Promoting the Game
The game store owner/personnel are key here, in that you have to depend on them in some regard, but you should be prepared to do all the heavy lifting. Here are a few of the things I did:
1. Make a nice flyer and bring it to the game store. Several copies are a good idea. Something colorful and eye-catching. Hang one on the bulletin board. Ask the game store to hand out the others to customers who they think might be interested and are also cool people.
2. Post about the game on blogs, facebook, forums, etc. Meetup.com has several local RPG groups, so those are a good idea to join and post to.
3. Mention it to people you know. Honestly, I'm kind of in-the-closet about my love of D&D. It's not something I wear on my sleeve. But I have mentioned my game to a select few co-workers and acquaintances who I thought might enjoy it.
4. Anything and everything else you can think of. If there are no players, there won't be a game!
Results: All of my game store players were the result of game store personnel promoting my game except for one cool guy that was local and learned about it through my blog. However, I still think it's important to go down all the avenues you can think of when it comes to recruiting.
Like Jeff said, bring a book or something with which you can keep yourself entertained in the event that no one shows up. If that happens, be persistent! There are people out there that want to play your game, but if you give up too soon, you may never meet them!
The First Session
I brought short player handouts with instructions for making 0-level characters (roll race, roll background profession, done!). I explained a bit about the game and my style of running it. I helped them get their characters together, gave them a very short synopsis of the setting, and gave them a few choices of places to go looking for adventures.
"We are playing Original Dungeons & Dragons from 1974. There aren't many rules. Feel free to try anything, and we will work out how to resolve success and failure. We aren't really here to have a serious, deep, and meaningful campaign. To me, it's mostly about hanging out with cool people, chucking dice around, and doing awesome stuff in the game."
"Basically you come from a generic Tolkienesque world, and you are in this newly discovered land full of ruins, treasure, strange peoples, and stuff you've never seen before. The main goal is to get treasure and stay alive."
"There are some caves over here (pointing to map) with weird monsters. There is a haunted house over here. Nobody knows whats over here. Theres a village over here with weird brown people, but most people that try to go there disappear. Someone said there's a ruined castle by the village, but no one is really sure."
I know that when I'm playing D&D, my eyes glaze over if the DM goes on and on with setting info that I don't care about. So I try to just give them the barest basics, and address anything else as it comes up in play. Try to get to the fun as quickly as possible!
Since we're playing OD&D, and getting a copy is stupidly expensive, I bring a few extra copies of Men & Magic that I printed up. The only thing it's really needed for is looking up spells. I typed up my own one-pagers for each class and the equipment list, but really the DM is the rulebook in this game. One nice side effect of players not having rulebooks is that rather than flipping through a book, the players just asks, "Can I..." That being said, if a player shows up regularly and shows interest in the rules, I'd be inclined to let them borrow one of mine to look over between sessions, and also tell them about some of the clones that are available.
Be careful about running a clone and asking the game store to stock a bunch of books on their shelf. There is a very real chance they might just end up collecting dust there, and you might not want to be the person responsible for that. If you run a clone it's probably safer to just have interested players order their books through the store if they want them. In my experience, a lot of players don't give a crap about the rules, they just want to play and be guided along as necessary by the DM. They don't sit around and pore over rulebooks outside of game time like a DM/D&D blogger might be apt to do.
Edit: Note that the last thing I want to do is discourage anyone from getting any of the excellent retro-clones available into their game stores. Just take into consideration that it can be easy to overestimate the demand for a game you might personally love. Maybe give it some thought before asking the game store to stock 10 copies of the game in question before you've even begun running your own game - that's all I'm saying.
Open Table Adventures
Since you have a rotating cast of characters, and usually a short amount of time to run a session, some concessions need to be made. You need to deliver fun, self-contained adventures.
I like to give the players lots of choices about what sort of adventures they'd like to have. I'm not hesitant to just flat out tell them, "that's the gonzo sci-fi dungeon, that's the haunted house, that's the traditional ruined castle dungeon, and blind exploration is available as well." The hope is that they can choose what they think is the most interesting, and we can get right on with the adventure. I think roleplaying interactions with innkeepers and locals can be quite fun at times, but it's not something you're going to find in my game store games unless the group decides they would like to spend the entire session doing that. There just isn't enough time in 3 hours to fit in that and a successful delve into a dungeon.
How I Roll
There are a few things I do at the table to help underscore the style of game I'm going for. I learned all of them from someone else more talented/smarter than myself, but they have served me well.
1. No Screen. We are all here to have fun together. To me, the screen is sort of adversarial, and a symbol that my notes, etc, are serious business. I haven't used a screen the entire time we've been playing, and I think it promotes the idea that I'm just another player that happens to also be running the game. I keep any tables and info I need at my fingertips in a little reference sheets-style booklet I made.
2. Keep the players rolling dice. This keeps them engaged. Aside from the normal stuff (attacking, damage, saves), I also have players roll wandering monster checks, damage their characters take, random treasure, monster crits/fumbles against them, etc. I rotate who is rolling initiative from round to round. Basically, unless there is a valid reason that it needs to be the DM rolling, I try to have the players roll. This also serves to minimize the player vs. DM adversarial aspect of the game. If a PC gets killed, I think it stings less if it was that PC's player that rolled the damage dice. At least it helps me to not feel bad about it!
3. I bring wads of d6s and roll monster hps at the table. It's a quick, easy way to track monster hp, and gives the players a bit of feedback about how things are going. They can tell the progress that is being made in a fight as I remove hit dice from the table. Most players can't see the actual numbers on the dice, but even if they can, so what? There's just kind of an unspoken gentleman's agreement that metagaming and trying to calculate your tactics based off exact hp numbers of individual monsters would be frowned upon. It's worked well so far.
4. Ask for player input. This is one I would like to do more often than I do, but I try to remember as much as I can. If a player asks to do something and it is not immediately apparent how to adjudicate it, ask another player how they would adjudicate! This is fun, helps keep players engaged, and gives players a chance to walk in the DMs shoes, if only for a moment. If one player asks for details about some dungeon feature you haven't defined, ask another player how they envision it.
5. Bring goodies. This is something I learned from Jim Ward. Bring goodies to the game! It is a nice gesture and helps promote the feeling that everyone is here to hang out and have a good time. I usually bring a few bags of kit kats, twizzlers, and the like. Perhaps you prefer more healthy fare. Nothing wrong with that either!
6. Roll a d6! I wrote about this on Google+ the other day, and it came about as the result of a discussion about fudge dice. Most simple questions in the game can be answered using this method. Does the equipment vendor have any pulleys available? Is there anything inside that dead monster's stomach? A result of 1-2 is a bad or negative result (example: poisonous viper living inside the intestines of that dead monster!). A result of 3-4 is neutral or indifferent. A result of 5-6 is a good or positive outcome (yes, he has 3 pulleys for sale, and cheap, too!).
7. Embrace randomness. I personally love randomness because it enables me to get a lot of the same type of enjoyment out of a game that the players do. I don't know what's going to happen any more than they do. To promote this, I build in a few minor extra rewards for players that make random rolls for certain things. For example, I give magic-users bonus XP if they randomly roll for their new spell when they gain a level. Dice can take the game in fun and unexpected directions. Let the players know why you think that is awesome.
8. The idea of balance is a mythical one. (This is more of a philisophical thing, and probably doesn't fit in this list, but I included it anyways.) There are two basic categories of things: cool stuff and dangerous stuff. The idea is that the players overcome the dangerous stuff and get cool stuff. We are told by a bajillion different people/sources that there must be careful balance maintained between the abilities of the PCs, the dangerousness of the dangerous stuff, and the coolness of the cool stuff. I reject the idea wholeheartedly. Not so much because I think it's wrong, but more due to the fact that it's a lot of time wasted on something I'm not very good at anyways. So I throw in lots of stuff that I think might be too dangerous and too cool, and let the players sort it out. You'd be amazed at what 6 players with their unused d30 rolls, a few wacky items, and a clever idea can accomplish! I've given out rings of 3 wishes, decks of many things, a lightsaber, an uzi, a few laser rifles, the sword of omen, etc. So what? That's all fun stuff, is it not? Most of these guys still have only 6 hp or whatever, so if they get too big for their britches, they will die. I used to have all sorts of concerns about "breaking" my game. One thing I've learned from playing Metamorphosis Alpha over the summer with Jim Ward is this: the only thing that can break my game is me worrying too much about breaking my game. (Note that this is not something he ever said explicitly, just my interpretation from playing in a MA mini-campaign, quite possibly totally misguided!)
9. Take a break. I always take a 5-10 minute break mid-session. The primary reason is that I'm a smoker, but it gives everyone a chance to stretch and has a nice side effect of getting the players browsing around the store. Hopefully they'll spend a few bucks!
10. Accessorize your game. Since you are playing an out of print game, it is a nice gesture to the game store if you can figure out a way to use some stuff the game store sells in your game. For example, you could integrate fudge dice into your game somehow if you have an idea for that. One thing I've done is have magic swords use different dice instead of having a +X modifier. So if you get a magic sword, you get to make your attack roll with a d24 instead of a d20. If you don't have a d24, you could just borrow mine or roll d20+2, but you want your own d24, don't you? What red-blooded gamer wouldn't? The d30 rule has made the purchase of d30's popular as well, if I'm not mistaken.
The Ongoing Game
At the beginning of each session, I let the players know about any other adventures that may have occurred in Outland (like in a G+ game or whatever). I think this helps create the feel of a living world, with goings-on outside of what the PCs are doing (with the benefit of having pretty much all the action still player-driven). I also consider one week to have passed between each adventure a particular PC has, and I allow them to start with full hp, and ask if there are any activities they would like to attempt during this downtime. For example, I've recently begun allowing magic-users to specialize in alchemy, so they can attempt to brew a potion or two - that sort of thing. If they wanted to study a book they found to see if they could get any useful information from it, I'd allow an INT roll, and so forth. There are a lot of things a PC can do with this time, and I leave it mostly up to the players to come up with ideas. Sometimes a player will come up with something really fun and you can create a simple little subsystem to handle success/failure, as I have done in the case of alchemy.
Well, that's all I can think of at the moment, but any comments or questions are welcome!