There are a ton of things. Wow. Eh, since people have talked about the more politcal aspect, I suppose I'll jump in with the musical stuff:
1. Make sure you are all playing in time---Time is a musician's greatest skill and the one that so few actually possess. Listen to everyone and make sure that you are locked dead into that groove.
2. Don't settle for less than the best---if your drummer just did a sub-par solo or rendition of the song, tell them about it. Remember, don't settle for just being an 'average' rhythm section--if you know that the people in your band are capable of playing better or bringing more to the table, tell them so! Get great performances out of each other.
3. Encourage everyone to sell themselves. Don't just stand there looking sullen and playing, look alive. After all, if you're a live band, it's not just the music you are peddling. I'm not saying you have to become CC Deville and smile like an idiot while playing ala Poison, but just look like you are having a good time. All of you.
4. Accomodate everyone's unique musical vision into the band!! This is so very important and the reason that a lot of bands have trouble. If you have a drummer who just loves Art Blakely, and you have a bassist that can't get enough of Rush, while your guitar player could rock out to metal all day long---use it!! Blend it, instead of trying to shape the music more toward your own musical tastes. Just because you hear your song a certain way in your head doesn't mean that that has to be the song you end up with. Half the time your bandmates will shock you with how much they can augment everything you do!
5. Sing. Everyone should learn how to sing. At the very least carry a tune. Why? Simply because of the huge amount of songwriting options it brings. You don't have to have a stellar voice to harmonize, sing backup chorus, etc.
6. Practice by yourself!! Maintain your individual competancy of whatever instrument you play. Increase it whenever you can. Your goal should be to have something new/different to bring to the table every time you guys meet for practice. The sad reality of the band is that everyone has to pull their weight, be profit instead of merely overhead.
I think those are the key musical tips to being in a band.
Back In Black isn't a song. It's a divine call that gets channeled through five righteous dudes every thousand years or so. That's why dragons and sea monsters don't exist anymore.