My $.02:
Practice the songs without any vocals because chances are you'll lay down the basic tracks like that. The singer can sing a scratch vocal track (one that will later be tossed), but depending on the studio the scratch track may bleed into the drum mikes. It won't hurt to be able to play the songs without vocals anyhow and be prepared.
In case you're nervous just remind yourself that you can always punch in (redo) anything you mess up on. If you make a mistake you don't have to stop the whole recording. If you don't like it when the song is done, but everything else is great, you can just punch in the spot you goofed on.
Don't be too quick to judge your own performance and try to look at the work (song) you do as a whole. Sometimes mistakes might turn out better than what you originally intended.
My group, The Nerve, just recorded last week and I found a neat new trick that worked for us. We wanted to leave the studio with 4 songs, so we recorded the basic tracks for six, knowing that we were going to chuck at least one of them. We wound up with 4 great (IMO) recordings. The pressure was off to be perfect on any one of them.
I keep pushing our new recording on the people here and I'm gonna do it again cuz it'a a good example of much of the above. I was nervous about recording this particular song because I never had any set bassline for it, I've pretty much imroved it from day 1. I goofed the song up from the very 1st note (as you'll hear if you listen), but nobody knows that cept me, and now I think it sounds great and works for the song. During the lead section I started by mistake with an E (instead of the A it was supposed to be), and once again something great came of it. The fact that I goofed badly freed me up for the rest of the lead section and I played stuff I never would have had I not screwed up. I didn't care cus I thought I was going to redo the whole part. There are about 10 other flubs in the bassline of this song, and nobody'd ever know if I didn't say, in fact I think they make me sound like a better bassplayer than I actually am. Hey - I'm divulging all my secrets here - oh well.
The song (if you want to hear it) can be downloaded with the big yellow button "F'd Up On Drugs" toward the bottom of our main page
www.thenerve.org.
Good luck.
Recording for first time 
