Basic Practice Suggestions
1) Take some time to warm up! It's much better for you to sing after warming up, even if you only do a few exercises.
2) Listen to the performance videos, even if it's in the background while you do something else. This is helpful to familiarize yourself with the general layout and sound of the song.
3) If you're going to do any intent work on your music, practice while LOOKING AT THE SHEET MUSIC! There's nothing worse than memorizing something incorrectly or learning the wrong part. If you always look at your music while practicing, you will learn it faster and with fewer mistakes.
4) Listen to your part tracks as often as the full performance. If you only ever listen to one or the other, you will only understand part of the whole picture.
Warm Up Exercises