Taking charge. Too many people are guilty, including myself, of being a passive GM. You need to be upfront and assertive. Don't accept a terrible sheet just because you accepted everyone else. If someone is being a little shit and bothering the rest of the players, kick them out of the RP instead of twiddling your thumbs and wondering why everyone is leaving. Try your hardest to stay focused on the RP i.e. post on set deadlines (this one I'm especially guilty of not doing) and being an active role in the RP (albeit without going overboard; let the players have some reign). Etc.