Bass Players - They're called quarter notes, learn how to use them. And in case you didn't know, you need to keep the time too.
Drummers - Where do I begin? Please play in time. PLEASE. When you're dropping beats or rushing rhythms everybody hurts. PLEASE listen to some soul/funk/jazz/anything with some heart and swagger and learn how to play TASTEFUL, RHYTHMIC, CREATIVE, AND STRONG music. If you look past your snare you'll find a beautiful thing called a ride cymbal. USE IT. Remember - you're making music, be musical.
Singers - If you can't sing. Don't sing. —Sore Ears