Monte Cook Games recently released a free 13 page PDF handout called "Consent In Gaming." The handout explains consent, explains how to handle breaches of consent, and gives a number of ideas on how to make sure everyone at the gaming table is having a good time and ok with the topic and subject matter of what is going on in game.
A lot of people are really happy with this product. Some people are less so. The interesting thing is that there is a subthread in the people against it whose argument kind of boils down to - as Rob Donaghue put it "I'm fine with consent, but we don't need it at our table."
There is this weird idea that a tool like a consent checklist is only for problematic people. Like, yeah, 'Weirdo Pete' should be told to respect these because he's a weirdo and does weird things. But I know my players and would never skirt that line. Besides, people should be made to feel uncomfortable at times, it helps them grow.
I call bullshit. Here's the thing. The characters in the game can, and should be made uncomfortable. The players should not. And note, I said "made." Some people go out of their comfort zone onpurpose to reach for things. That is for them to decide. But if someone is uncomfortable with 'on screen' torture, and you put it into your game knowingly, you're not being a "good game master" nor are you "challenging the character" or "inciting growth." You're not even being "edgy." All you're being is a jerk, and you're abusing a position of trust and a power dynamic to inflict emotional stress on a player.
Now I'm not saying everyone needs to go out and download Monte Cook's handout, or use the questionaire for their games, but it is a damn useful tool to have when planning a game. Why? Because beyond the obvious of showing you what areas of content your players don't want to go into, it also tells you where they want to go.
You have a group of players who aren't much for body horror and insects, but are all for blood, gore, and violence? Damn, that sounds like a really useful thing to know when planning your game. Now you know you can go nuts with the Slashers, but just need to keep things from going full SAW and you have yourself a Halloween game.
This is good for any game and for any group. Even people you've played with for years may be in a place mentally where they're not keen on things they previously weren't keen on. I know people whose tolerance for injury to children dropped way down when they had kids of their own. It wasn't that they were monsters who'd hurt kids before, but they couldn't detach the kid in the game from their kid and it made them uncomfortable.
You can do it however you want. You can use whatever tools, avenues of communication, and relationship/social networking you want. But games run better when everyone at the table is comfortable.
Also, the Monte Cook "Consent In Gaming" is free, and is worth a read even if you don't plan on using it. Maybe you'll learn something. Maybe all you'll get is a few references to some interesting games out there.