[quote=@BrokenPromise]
-You can't waifu them all, don't even try. 
[/quote]

i beg to differ

--

Serious contribution to the topic: If I GM, my preferred way of getting people to do stuff is to put them all in the same room or general area, and give them 1-3 things to do, depending on group size and types of characters. Everyone will gravitate to an event and naturally form bonds; whether those become cliques later is a problem to deal with down the road. Generally I like to be as loose as I can with my players, though, unless someone is actively fighting against what the collective wants to be doing and is clearly not engaging with the bigger picture.

As a player, though, if I don't immediately have something I can insert my character into, I just talk to people and ask around what I can join with them. There's usually someone that isn't doing anything, and even if there isn't, there's usually a way to get your character involved in a group activity in some way. Sometimes I'll even just solo with the GM for a bit if my character starts in a far-off location, but the end goal is then to contrive me into the group at the end of that tango.

Usually I've never had too much trouble getting characters to interact, but that may be down to my personality of just being very involved in the going-ons. I'm not the most vocal person in any RP, but when I do speak up, it's usually to plan something out for the IC or asking people if they want to post. As broken said, just communicating does most of the work.