try holding it taut not tight, go slow to start, and also try angling the strop slightly (as in along the direction of draw looking down the strop), some guys find this makes it easier to contact the blade properly. concentrate on the spine as others have said, and i wouldn't use any pressure other than the weight of the blade to begin. also blade contact in stropping is just as important as in honing, you can risk dulling the blade otherwise.