I used to have troubles with it too...
I searched on here and found a link to this youtube video that helped me:
http://www.youtube.com/watch?v=Of5Eas6lONM
Generally I start off on the plastic and just fast swipe and it works great. there are other ideas here in this thread:
https://www.mobileread.com/forums/sho...ht=swipe+video
For some reason though - watching the youtube video seemed to help me most since I'm a visual learner.