Workflow!

[Tweakhead]

Most of these tips are very good and are practised by many engineers. One additional one I would add would be this:

After you have comped your final vocal, if time permits, give the singer/artist a copy of the song with the "finished" vocal comp to listen to overnight. Then let them come back in to the studio another day and sing the entire song down in several fresh takes.

You will often get a fresh, inspired, dynamic, performance-based vocal out of them that will outshine the comp. They will also feel empowered that they are allowed to create a flow for the song. I have done this several times with very professional singers, and they often love it - and rise to the challenge.

The reason this approach works is because the artist is having to create a vocal for the very first time during the initial tracking stage, and they have no reference point for creating a new vocal. Let them be artists.

[DrFord]

I have to add one more tip, not to be ridiculous and overbearing here, but a surefire way to get your final vocal with reduced budget groups is to say...
"I can't justify you coming in for a 4th time to re-record vocals at the current budget. You can either open up your budget and pay my full day rate or be happy with the best of the current recorded material."

I just did this and the budget expanded by $200 for 4 hours of vocal overdubs. I seriously doubt they will be able to budget another session if the vocalist still isn't happy with his performance.

Now this will of course become 4 additional hours of after hours editing / tuning / retuning / re timing, but hey, at least they increased the budget. Allow me to qualify this as a "favor" I am doing for a local band with a reduced budget... "Sure I'll do your project for X," and a month later X has become not worth while.