1- Keep track of your vocal provider's position. Make sure the position the provider provides vocals is the same each time he or she comes back from a break to continue recording. Ensure the vocals are coming from the same position each time.
2- Many vocalists sing better when they tilt their head back a little, as it opens up their vocal chords.
3- Have a clear idea of where a certain line is to be placed. Example, the word "love" in a verse has to hit right when the "snare" is heard.
4- Applying a chorus effect is ok, but the best way is to recird multiple takes of the vocal,mixing them together.
5- External sounds like coughing and ice knocking against the inner wall of a glass can sound cool when compressed, Try it!