I found that prior flight training was extremely effective-
Flying a parachute is a few big steps down in complexity than flying an aircraft. It took about 10 jumps to get the flare stabilized... and about another 15 to dail it in pretty well. I started experimenting with front risers at about jump no. 5 or so. My call on that one though...
There is a detail here... just because someone can fly an airplane/ glider dosen't necessarily mean that they are good at it (ie they lack practice), and thus will not have the skill base to transfer over. If you've developed the judgement (in various fields- timing the flare, pilot decision making, risk management) you'll have a strong skill set to apply to jumping. If you're 20 hours into a PPL, don't expect to be too far away from square one when it comes to jumping.
Because it's relevant: flight sim's do help... a lot. Learn how to fly 'normally' there, and then learn how to push it in the sim too. Crash. Find the limits. It hurts a lot less that way. Granted there are limitations, but the benefit is greater than nothing.