Previous: 7. Comp your lead vocal.
Explanation: These go last, because they must mix smoothly with the lead vocal. If the soloist chooses to be freer with timing, phrasing, and pronunciation, you want to base your backing singers on that performance. Otherwise it can get quite messy.
Make sure that the singers are also in sync and in time with each other. They should have a clear knowledge of what they are singing, based on the written score. Don't rely on " figuring it out" as you go, but don't rule out a brilliant variation that someone may come up with on the spot. The goal is to get the best tracks you can.
You can do the all the backing vocals yourself, too. Just record a few takes, and then they will mix like a choir. If you are a guy, you can do some tracks in falsetto, to sound like you have women in the choir too. It's a neat trick. Women can sing takes in the higher and lower octave, for variety. I usually do four tracks for each harmony part, which you can then pan nicely for stereo effect.
Some prefer to record the singers together, others prefer to record each backing singer track separately. Do what ever gets the best, most together, most polished results.
Next 9. Begin mixing by creating a rough premix.