1.) Practice, practice, practice. Before you go to the studio, do your best to get as much practice with the songs you plan to record ahead of time. You really can waste a lot of time when you have to do multiple takes on your verse. Average song should take no longer than one (1) hour. 20 to 30 minutes recording and the rest of the time towards mixing. If you take longer to record your voice than the engineer takes to mix your track, then you are wasting time and money.
2.) Unless the engineer gives you direction, then your mouth should be 6 inches from the pop filter and the pop filter should be 3 inches from the microphone. Most engineers have a setup preference, so don't be afraid to ask the engineer.
3.) Breathe control. Breathe control is important every time you open your mouth to start rhyming. Whether you are up on stage or in the booth. On stage, breathe control can be the difference between an outstanding performance or a wack one. In the booth, breathe control or the lack there of can be heard on your vocal tracks. Yes, it's true that engineers can add plug-ins, filter, gate and noise reduction. But, for every effect that is added to your vocal, a natural effect in your voice is taken away from the vocal.