AD&D1e: open game table

The first of the house rules is to have an open game table. Any player can come or go at any time. The reason for this is accessibility: if you want people to try your business, product, service or game, you must make it as accessible as possible. Many gamers hold an ideal in their minds of the same group of 4-6 best friends gaming together in some grand epic campaign over 10 years. This is cool, but rarely actually happens. Most commonly a group gets together, and about a third of the time they spend their first session generating characters and the group never meets again, the rest of the time they play for 12-18 sessions before enough players get bored and drift off and the game is suspended indefinitely. 

Better to accept that players will come and go, and plan for it by having a constant supply of new players - you need accessibility. 

Accessibility means a few things,

• Advertising: Before anyone can come, they have to know about your game. When I first started gaming in the 1980s I put a sign up in the local library next to all the Choose Your Own Adventure and fantasy books. Nowadays it's much easier, there are endless groups on social media and in forums where you can talk about gaming with local gamers. If you're planning a game, start talking about it - discuss the system, your house rules and so on. By the time you're ready to go a few weeks will have gone past and they'll be used to your name and ideas. 
• Place: if possible, don't look at libraries and the like, but game where there are other gamers. Most Western cities have game clubs or cafes, commonly focused on card games (which pay the place's rent and salaries) or board games (which don't). Wargame and miniature clubs may also have a spare table or two. Don't worry if there are no current rpg groups, you'll find most geeks are happy to try all sorts of hobbies. 
• People: game with whoever shows up, and if anyone stops by your table, greet them, they'll no doubt ask about your game - tell them briefly and enthusiastically. Do not conduct lengthy interviews "to see if they're suitable", give them a written Social Contract to sign, blather on about varying playstyles or any of that self-indulgent nonsense. Just have them sit down and roll up a character. Man, woman, uncertain, young, old, suave, dork, Magic the Garnering player, even god help us a storygamer, doesn't matter. Get them to roll up a character, and offer them some of your snacks. 
• System: obviously here we are talking about AD&D1e, but the reason we're talking about that system is that it's accessible, a magic-user character can be made in 9 dice rolls (the 6 attributes, hit points, starting wealth, starting spells) and a fighter, thief or cleric in 8; the slowest part is choosing starting gear. Thus the newbie player can go from saying hi to being ready for play in under 10 minutes. That's accessible. Games like Classic Traveller are also accessible for newbies.
• The Game Must Go On! in your open game table advertisement, choose a place and time slot that suits you and then... stick to it, no matter what. Don't run around asking everyone what'll work for them, 5 people will give you 6 different answers and you'll make 30 phone calls trying to arrange it and then only 2 of them will show up anyway. But if you set a time, 3-4 of those 5 people will come. For example, "Tuesdays at Game Club Woop Woop, 6-10pm." If nobody shows up, sit there and make some more DM notes, circulate around the other game tables, and talk to people. If one person shows up, great! You give that person the best game experience they've ever had in their life! They get all the XP! The game must go on! But...
• Limit it. I already mentioned finishing the game on time or slightly earlier, but the campaign as a whole should go for not more than 12 weeks. You limit it to keep yourself fresh as a DM. It's going to end at some point, better to plan it to end than having it eventually fizzle out. Think Babylon 5, not Happy Days. Take a break of a week or two and then have another go, doing something slightly different - use another system, go to a different game club, whatever. As well as keeping you fresh, limiting it keeps players engaged - in any group you'll have people who are super-keen, but also some people who are just sort of enjoying themselves. If these lukewarm ones see no end to it they'll bail, if by session 8 they're content but not thrilled, they'll stick around till session 12. 
• Stay in touch: Finish the game at the scheduled time or slightly before, thank everyone for coming, and say the game is going on next week and they're welcome to come again - and bring friends! Give them your mobile number and email, and get theirs. The next day, email everyone who came and thank them again, and give a brief rundown of what's happened in the campaign so far, and again invite them to come next week. Leave it at that. If you take a break from gaming and want to start again, the first thing you do is email everyone who's ever been to your game table and ask them to come again. 

In practice if you advertise things well and are welcoming enough, you will get a lot of players churn through in the first 3-5 sessions, and then after that it'll settle down into a fairly steady group of 3-6 players. In one Classic Traveller campaign I ran over 12 sessions there were a total of 10 different players, one came to all 12 sessions, one came just 1 session, and the others came to a bit under 8 sessions each. The most players I had was 9 in the 1st session, and the least 3 players in the 4th and 8th sessions, we averaged 5.6. 

I did some other stuff, and the following year I invited most of the previous players back for a second go. Running that second CT campaign of 13 sessions, we this time got very similar results - 10 different players, one coming once, one coming to all 13 sessions (the same one as came to all 12 the year before), and the others doing an average of 5 sessions each. Three of the sessions had 6 players, the fewest was 3 players, we averaged 4.3. 

Obviously once you have that steady core group of 3-6 players, you can if you want run a closed game table. I don't recommend this - in the examples above, 3 of the 10 from the first CT campaign came back, others had either gone interstate, moved too far away or the like, or didn't reply, and one I didn't invite because he had been studying orbital mechanics and wouldn't stop arguing about it. With just 3 of the players, if even one person is absent one session things can slow down a lot, if they move or change jobs or make a baby or something then they're gone and you're stuck with an empty game table. But from the first to the second campaign, 7 new players showed up. 

Given that however awesomely you do everything, players will inevitably come and go, you need to have a constant influx of new players to make sure you have a full game table. Steady tight groups can be fun, but they can fizzle when 1 or 2 key members leave, and they can turn stagnant with the same people playing the same roles and telling the same jokes over many years. 

Keep it fresh, have an open game table. Set a time and place, advertise it well, choose an accessible system, stay in touch with people, and always remember: the game must go on!