The value of a formal contract is recording agreements among all participants to ensure everyone understands what is expected. Obviously, a long written contract will make most players' eyes glaze over and kill the fun. Maybe just have a discussion about some things. If you have a widely fluctuating set of players coming and going, a written contract can help new players assimilate quickly.
A formal social contract covers all details of play. Specifically, it is an agreement to play a certain game, at a certain time and place, with certain people, in a certain way. In other words: what, when, where, who, why, and how.
What
- What game are we playing?
- What version of the rules?
- What house rules?
- Can house rules be introduced later? By what process?
When
- What is the game schedule? Weekly? Every other week? Monthly? Irregular?
- What are the exceptions to the schedule?
- What is considered "quorum" for a game? (Under what circumstances will you cancel a game?)
- What is the process for formally cancelling a game?
- How should players notify people if they cannot play? if they can play?
- What is the process for formally inserting an additional game outside of the normal schedule?
- How long do we play (per session)? Will that change often (extended games), or do we need to stop at a certain time?
- How long of commitment are you expecting? One game? Three games? A year? Forever?
- Is it cool to miss games? How often?
Where
- Where is the game hosted?
- Are hosting duties shared?
- What is the address of the place where we play? Got directions?
- Where do we park?
- What are the special rules of the house? (take off your shoes, don't let the cat out, etc.)
- What should people bring? (food, dice, books, miniatures, etc.)
- Will we eat during the game? Who brings the food? How is paying for delivery food handled?
Who
- Who is invited to play?
- Who is excluded from play?
- What is the process for inviting new members?
- What is the process for bringing a friend or significant other to a game?
- Are children or spectators or pets permitted as tag-alongs?
- What is the process for correcting poor player behavior?
- What is the process for expelling someone you don't like?
Why
- What is the point of play for this group?
- What is the general mood of play? (fun, serious, dark, etc.)
- What is the general theme of play? are there any special tropes?
- Is it okay for players (including the GM) to be competitive with each other? (up to killing each other's characters?)
- Are there any limits about game content ("lines and veils")?
How
- How do players create characters?
- How do players advance characters?
- What level of playing "in role" is expected of all players? What is too little? Too much?
- What is the expectation around character death? Under what circumstances can it happen or not happen?
- If a character dies, how does the player replace it?
- How do players integrate characters into the setting?
- How do players integrate characters into the game's situation or existing character group?
- What kind of play behavior is considered annoying?
Also take a look at Chris Chinn's Same Page Tool.
I can't give you a full list of the occurrences, because they are sprinkled throughout, so I'll focus a bit on why those two examples are expressly called out as deciding them before play.
The reason these are called out is because they have the potential to hurt feelings and cause heated discussions at the table.
Lawbreaker example
First example being the lawbreaker rules. If you break a law of magic, you immediately gain a stunt that costs 1 refresh: Lawbreaker [law number]. Many wizards are probably skirting the line with only 1 refresh remaining, so if they break a law, they are immediately in NPC territory. Thus it's a really really good idea to hash out in your game what precisely constitutes a law violation.
For example, if you burn a building to the ground that might have humans in it, and some of them perhaps died in the crossfire, does that constitute a violation of the 1st law of magic?
Now, you can probably get away doing this during play, so long as you warn the player that he/she is about to become a lawbreaker, and that no further warnings will be issued, yadda yadda. However, I feel that everything goes more smoothly if you hammer this one out before play. Even if you do this, though, you will need to make sure the group is okay with a single player being the final arbiter as well.
Death as a result of being taken out
This is less important, I think, as you generally as a courtesy should inform the players that a given conflict could wind up being lethal before the dice are rolled. That gives them the chance to offer a concession before they, you know, die. You might want to lay out some ground rules with your players first like: "I'll let you know if you think you're likely to die in a combat." Or "I will not inform you if you are going to die as a result of combat, so please keep your wits about you." That way you don't run into any issues when some of Johnny Marcone's thugs come to beat their heads in with baseball bats.
Some other examples
- City and Story themes: These are explicitly defined by the players in the first session, and thus have to be done before play begins.
- How nasty a sponsor for sponsored magic is likely to be: That way the player knows what they're getting into...or that they really have no idea what they're getting into.
Best Answer
Some questions to answer in your social contract:
Can my character die without my consent? In D&D (and most action-based games) the default answer is 'yes'. Subquestions to ask: Will I get a hint that I'm in serious danger? (In 4e you usually won't need one... it'll be obvious that you're low on surges and survivability.) How likely is this? (Players in my games know that I will kill characters, but it hasn't actually happened more than a couple of times in the last 10 years. The possibility is enough.)
Can my character die as a result of a single failure? Are there effects which kill or disable you at once if you fail a save, regardless of your state of health otherwise? In D&D 1 the answer was 'very much yes' and each edition since has been less so - a very good thing IMO. 3e in particular made a deliberate effort to reduce this, 4e more so - so in 4e you can say 'no' with no real change.
Can my character die as a result of another PCs actions? D&D mechanics assume a social contract in which the group are all on the same side, and in 4e this assumption is very strong. But good stuff can be done with characters that are mostly on the same side; conflicting goals -> character development -> entertainment. So: Might another PC abandon the group during a fight? In particular, especially in D&D, cover can other players kill my character? as an entirely different question from whether the game world might. D&D 4e assumes 'No' as a default here, and 3e assumes 'very unlikely'.
[Edit/added, thanks to Valadil:] Can my character die when I'm not present? If a player can't make it to the game, does their character vanish, or get played by other players, or by the GM? It's demoralizing to have a character killed or permanently damaged when you're not there. (Our group uses: GM tries not to kill the character when the player isn't there, but only if players refrain from using the PC as invulnerable point man... PC actions are by group consensus, but the PC does nothing especially heroic or dangerous. Basically, a no-score draw.)
Can my character be resurrected once dead? In D&D the default answer is 'yes, at a cost', if you're high enough level. In 4e the default answer is 'yes, at a not-high cost', especially in LFR. (Look at these rules; in a home campaign they have implications for the game world. We play LFR adventures... but the LFR resurrection rules seem too cheap to us; we multiply all costs by 10.)
Do the rest of the group have to try and resurrect me? In D&D, a regular party might even have in in-game contract for this one. Be sure it specifies who pays!
At what level does my replacement character join the group? (Our long-standing D&D and Star Wars answer has been 'at the bottom of the level below your previous character's level, plus some bonus xp based on how you roleplayed the death scene'. Another common answer is 'Same level as the lowest-level character in the group'.)
What non-base abilities/equipment can my new character have? In D&D in particular, magical items are the issue. 3e and 4e assume a certain level of magical item power for any given level of character; al cash value by level can be an acceptable guideline but not a dramatically brilliant one. In D&D for mage characters, you also need to consider 'How many spells does a new wizard know?' (in 3e) or 'How many rituals do I have?' (in 4e).
Adventurers being adventurers, and depending on your group's play style, you may also need to ask if my character dies, do the party loot the body for useful magic? (GMing note: Having an unknown relative show up and lay claim to the deceased PCs possessions is a fun way to cause trouble for item-oriented groups... especially if they had a mission-critical item at the time.)
The Living Forgotten Realms rules cover all of this well and are worth a look, but don't use them as a model for a regular group. They're designed to handle a situation in which you're playing drop-in convention games with random strangers and want the GM to recognise existing characters. They do a decent job of examining the kind of question that can come up.