Any tips/Adive about playing in a band?

Great topic. I have quite a few suggestions. Since you're a band-playing noob I'll start with three very fundamental things.
1. Tune with a tuner. I know this sounds silly but trust me - when you're in a room with three other instruments, it gets really hard to hear yourself well enough to tune. Trust technology and you'll all be happier (and sound better).
2. If you guys are reading music from chord charts, make sure you are using the same version of songs from the same website, etc.
3. CRITICAL: Develop a no interruptions policy. There's nothing more irritating than trying to work out a line or chord changes with your other guitar player or bassist, meanwhile the drummer is pounding away making it hard to hear. If you aren't playing a song together and two people are trying to work something out, everyone else should remain quiet and off their instruments. (That's just good manners.)

More advanced stuff:
1. There's a big difference between band rehearsal and practice time. In order to use your together time more effectively, every member should know their songs and their parts before you try to play them in the rehearsal room. Show up knowing your part and your will use time more efficiently.
2. Lots of new players spend time listening to themselves in the band. The result of this is that the band doesn't really sound together. You should focus on the other players before yourself - if you've paid attention to #1 and already know your music you shouldn't really need to hear yourself. I try and focus on (in this order) bass drum, high hat, bass guitar, everything else, me. (unless I'm soloing in which my attention turns to tempo [high hat] and harmony [other guitar/keys].)
3. When you are playing solo there is only you to fill space. In a band there are several other players. If everyone is playing at 100% all the time it will sound like a muddled mess. You need to allow space for one another, which you'll be able to identify via #2 (listening). In addition to knowing the right notes to play you have to know when it will sound best to sit out or reduce your playing. (There's a quote attributed to a great musician that says "a good musician knows what notes to play. A great musician knows when to not play.") I played many a gig just singing, with my guitar volume turned all the way down.
4. Make the songs your own and have fun!

-BGD

Decide what you will play get one member to play it through just the rythm. Then you all know whats suposed to happen .Dont be phased if some one says the original or sombodys version  doesnt go like that.unless you are a tribute act it doesnt have to be identical ,put your own stamp on what you do.
Make sure you are all in the same tuning and know what key your playing in also its in the right key for the singer.Be aware that the singer may want to  go up or down a key so prepare your self for that.I remember one band I played with and the singer turned to me as we were about to start the first number and said we'll play this in f sharp tonight which completly threw me and it took me a verse to figure out where the song was going and where to play the lead breaks.Most of all practice all your songs prior to rehearsal so you know whats going on and if possible record your sessions so you can see how you progress.Good luck and I look forward to hearing you

All great advice and do keep us posted. Lots of very kind help here.

Bill

Use the bathroom before going on stage.

We don't play out but the trio that I play with usually has one person start the song with a chord or a couple notes then the other 2 jump in. Everyone ending together can be tricky in the beginning but after playing together for awhile you can start reading signals from each other.

If you watched the videos we made at the Pa gathering you might have noticed that I got lost in the middle of a couple of the songs. But the other people that were playing kept going and I caught up. Most folks never noticed.