1) Moving the main gear back some will help. Being too far forward exasperates the tendency to ground loop, plus it makes it more difficult to raise the tail on takeoffs.

2) Anticipating the ground loop will help. Think ahead of the plane.

3) Not over-controlling will help. Small, gentle movements of the rudder stick. And increasing expo on rudder will help some.

Try #2 and #3 first. If those don't fix the problem, then look into #1 (if moving the main gear back is feasible).

edited: For reference, here is another thread on this topic: Ground looping