Getting the band together!
Role-playing is a collaborative activity! How do you get players to create characters that function well together as a group. I've played with a lot of groups where everyone has a very strong idea of what they want to play, even if that doesn't mesh well with the other player characters, some players just get that target fixated. I do tell my players that they should keep an open mind and revise their concept if it doesn't work well with the rest of the group, of course!