In the words of Dennis DeLucia, "Keep Your Grace Notes Down!"

When playing flams, we often see players lifting grace notes and not playing with the correct height separation. It is YOUR JOB, not your teachers job, to spend time isolating your height separations from beat to beat. Make sure you take flam passages slowly and use proper stoke types to maintain great placements of grace notes as they relate to the music you're playing!

Attention to detail is what separates the good players from the great players. Which one do you want to be?