Agree on tightening the cleats you will have all sorts of trouble if they are loose and you may not be able to unclip at all, very dangerous. Thats happened once to me and was quite scary.
I've used 3 clipless systems Crank Bros being the best and Wellgo the worst and I find it's stepping downwards into the peddle after lining up the peddle and cleat is the way I learned to clip in.
I actually learned by leaning up against a wall in my hallway, an hour of swearing and shouting and suddenly it magically happened. You may want to go back a step and practice getting the weaker foot in when stationary. My right foot seems to be my harder one if I'm using a new set of cleats say so I still have occasional issues.
Clipping out should just be a simple twist, it might be because both cleats and peddles have not been broken in, try a dab of lube on the peddle also.
A use lithium grease on the screws, like you I'm quite heavy, so far no issues with drilling out the screws.
Last edited by Jonahhobbes; 09-21-09 at 06:05 PM.