S - Sing through your vocal weakness and breaks
The only way to learn singing perfectly is to sing through those portions that you find troublesome. You need to train your muscles. You won't achieve success till you sing through those portions again and again till you are perfect.
I - Increase control over your breathing.
To do this you need to practice breathing exercises on daily basis. To achieve versatility you will have to start breathing for different lenghts, you can compromise with a patterned breathing.
N- Never sing if you have a sore throat
Yep, dont try to be brave or give in to a request. Your voice is priceless, don't damage it for just one evening.
G- Guessing Pitch.
Dont try to guess the picth of the song of you are about to sing. You should have note read out in your mind before you begin.