I don't actually recommend explicitly drafting a social contract. It's a little too... I dunno, it's a red flag for me if there's a need to do so. But at the same time, it's worth giving some thought to what the elements of that contract are, and what you believe them to be. Here's a list I found in an old forum post from long ago that lists a number of elements that a social contract—even an implied one—could have. Hopefully the maxim "Don't be a jerk" already covers many of these, but others of them it does not, and some clear expectations certainly can't hurt.
- The game system or edition to be played;
- Supplemental materials that will be employed or specifically ruled out;
- Explanation of DM-created house rules that will be used;
- The number of players, and a process for adding new players or "writing out" players who leave the group;
- Logistics of meeting places, provision of snack foods or meals, or sharing expenses;
- The expected duration of the campaign;
- Meeting days/times, session frequency and duration;
- Attendance expectations, and what happens if a player is chronically absent;
- Procedures for canceling a session;
- The overall tone of the game, and expectations that characters will contribute to that atmosphere instead of undermining it;
- Table conventions, such as how often a person can speak out-of-character or, my personal favorite, the you-said-it-you-did-it clause, for players who try to make everything into a joke;
- A stance on whether or not player characters may attack each other;
- Policies about note-passing, whether or not die rolls must be made in plain view, and ethical concerns such as allowing evil player characters;
- Procedures for handling player-DM disputes; and
- Rules regarding physical contact between players.
Some of the other items, like expected duration of the campaign—well, that doesn't really need to be spelled out, but it can't hurt to have an idea before you start. It's not necessary, but it's still a good idea.
I'd say my own preferred social contract goes something like the following, with details not included, as yet:
Welcome to the DARK•HERITAGE game! The game will be run using the m20 system, which can be found online, or I can provide you printouts at our first session. It's a fairly rules-lite system, which means that GM rulings will be an important part of the game. We'll play every other week on yadda-yadda day at blah-bitty-blah-blah time. The m20 session allows for up to ten complete levels of play; once every player has hit tenth level (if not before), the game will start winding down for its eventual conclusion.
As GM, my purpose in bringing this game to you is to entertain you for a few hours every time we meet. As in any good story, entertainment happens when crappy things happen to the characters, and they have to deal with them. Keep in mind the tone of this game, which is meant to be swashbuckling and action-packed, but also laced with an element of horror and noir. Characters aren't expected to be heroes, and the game could be a solid PG-13 at times in terms of content. Characters may not always get along—just make sure that any conflicts remain between characters and not between players and we should do OK. Don't identify too much with your characters. While I may "punish" your characters from time to time, I'm not attempting to punish you in any way, and the intent is to create situations that are interesting and fun to explore.
Please feel free to give me feedback; I want to make sure that I'm providing the best experience possible for you and your fellow players. Just keep in mind that the game is, of course, about all of us and we may have different things that we like about gaming. I'll try and make sure everybody gets their "moment in the spotlight".