Providing group cohesion is a priority for all our game designs at VSCA though each game goes about it differently. Some of these methods are very portable to existing games, so lets have a look:
In Diaspora it's implied (and in future revisions will probably be more explicit) -- the characters are somehow bound to a single space craft (as crew, passengers, whatever) and so the state of the craft is a group interest from the get go. It helps that outside the ship is the hostile environment of space, so ship troubles matter to everyone.
In Hollowpoint it's an explicitly state premise of the game: characters are all members of the same team on a particilar mission. There is no motivation to act alone and, even if a scene is narrates with some characters acting alone, mechanically the scene remains the same so there is no hardship in it. This is harder to transplant to another game,
In No Contact (unfinished) characters begin as mmbers of a lost fire team in Vietnam and have selected specific roles in the team. Because military units have roles that are interdependent, explixitly pointing out the role of each chqracter (the radio guy is the contact to home, the heavy weapons security carries the ammo and watches the hwo's back, &c.) creates a natural cohesion without specific mechanisms for it.
So there's three ways: a common interest, mechanical cohesion, and interdpendency,