This article is based on problems I've encountered repeatedly when mixing peoples' home-recorded tracks. It may seem full of some super-obvious stuff to some of us, but these things come up over and over again and could have easily been headed off at the pass, even by a first-time recordist.
1. Use (beg, borrow) the best cymbals you can. Programs such as Drumagog can fix bad drum sounds somewhat later on, but crappy cymbals are not going to improve much in a mix.
2. . If you can hear the air conditioner your mic probably can too. So shut it off while you are recording. (Then be sure to pay attention to the effect a change in temperature might have on your tuning, of course.) This goes double for the dishwasher!
3.Intonate that bass guitar before the session! (And all guitars.) If the bass is out, even on one string, everything higher is going to get wonky as you overdub, singers included. Your local guitar store can do this for cheap if you aren't sure about which way to turn those little screws on the bridge. Keep a tuner inline with all guitars, and ask everybody to retune after every take if there's time. You might need to check to see that all the different tuners agree, as well — there can be a lot of discrepancy between equipment.
4.If you are recording a vocal in a bedroom or other untreated room with a directional mic, try to make the space behind the singer's head acoustically absorbent. Even if you don't have panels up, at least keep away from windows or mirrors.
