Here's a little variation on the advice that I haven't heard anybody mention so far:
1) Everybody warms up with a metronome or click track. Yes, everybody, not just the drummer. The whole band's sense of time will improve.
2) Have the rhythm guitarist lay down a pilot track to the click.
3) Have the drummer record a track while listening to both the click and the rhythm guitar pilot track. That way he has both a guide for perfect timing (the click) and he knows where he is in the song (rhythm guitar) which allows him to toss in the occasional fill to taste.
4) Have the bassist and rhythm guitarist record their parts while listening only to the drummer's track....no clicks or pilot tracks.
I have found that with both myself and other musicians in the studio, this can be a painless way to get the steadiness and accuracy of playing to a click and just enough live groove to wiggle a little bit. I haven't met the person who can actually groove while a click track is playing, which is why I have you record your bass and rhythm guitar to just the sound of the drummer.
Once that core of drums, bass and rhythm guitar is set, you have your foundation. You can double up on guitar tracks, do guitar leads, punch in drum fills, whatever....to your heart's content.
BTW, a similar concept can be used to help the lead singer nail his vocals:
1) Set your drum, bass, and rhythm guitar foundation as above.
2) Have your singer record a pilot lead vocal track. Have him do it as straight as possible with no flourishes, no grinding in the voice for emphasis, no scat singing or ad libs. You want this track to be both as boring as possible and as pitch-accurate as possible. Have the singer focus only on getting the pitch as perfect as possible. No spice to jazz it up...this isn't the final track. It should sound like a 9th grade choir with perfect pitch....bland as can be.
3) Have your backup singers (including the lead vocalist if he's doing backups) record their track while listening to the lead vocal pilot track. Having a perfect-pitch lead track is much easier to harmonize to, and it will help the backup vocalists place the proper emotional emphasis at the right time(s) in the song.
4) Finally, have your lead singer record his actual lead vocal track while listening to the drum/bass/rhythm guitar foundation and the lead pilot track and the backup vocals at the same time. This will give him both the timing, pitch and lyric cues as a safety net, and it will give him the confidence of singing along to an already-existing vocal, just like he does in the car or the shower where he can really belt it out without being self-conscious. This time he can let loose and sing it however he actually wants it to be on the final recording.
BTW yet again.....notice that I haven't yet mentioned the lead guitar solo. That is on purpose. Unless your lead guitarist has an exactly composed solo already in mind, it is often best if he waits till everything else is recorded before he lays down his solo track. Just as with lead singers, and sometimes moreso, lead guitarists often need to feed off of the total energy of the song to tap into their greatest inspiration for the solo that really fits the energy, groove and vibe of that song. The more your lead guitarist is a one-take, off-the-cuff, pure improv kind of guy, the more this will benefit him.
Good luck and have fun with it.