Remove the tape immediately after you are finished painting. This will help prevent paint from bridging over the tape and tearing when you remove it. When latex paint begins to dry, it becomes rubbery (like a rubber band) and has a tendency to pull.
Remove slowly, folding the tape almost all the way onto itself.
If the new paint does begin to tear, gently score the edges with a razor blade.
If the tape begins to tear the wallboard when it is being removed, this likely means you have masked on a poorly bonded surface. Try softening the tape's adhesive with a blow dryer.