Practice, practice, practice.  Everyweek I practice a couple of games where all I do is cherry pick the 7 and the 10.  It really is that simple, once you find a shot that converts it, you need to train your body to repeat that blasted shot every single time.  You'll miss one on occasion regardless, the best do as well, but if you shoot an extra 20 10 pins a week, it won't be long before it's a spare you become almost automatic on.  A fun way to do this is golf bowling with a buddy, lowest scores win, gutters count as strikes.  If you finish a game in the 30's, your doing pretty darn good.

You'll put yourself easily into the 90-95 percent range if you do that every week, if not the 99% range.  There is no trick in the book that doesn't work without practice.  Find a spot that works, and shoot the hell out of it.  I was like you, shooting 65-70% on them, but once I started the practice, the % jumped.  I've recently had sets where I've gone 12-12 and 14-15 on tens respectively.