Originally Posted by Disco Stu
I suggest recording a rehearsal or at least a few of the songs with the most problems and having your bandmates listen to them. I think a lot of players find their mistakes or weaknesses more glaring when they aren't playing and are just listening to themselves. Maybe that will motivate them to improve.
Yes, this is what helps out groups that I'm in, more than talking to them about it or trying to set an example.