Re: casting weighted flies
I think first you need to be sure you setup is good. If you are trying to cast big heavy flies you may need to use a heavier rod and line. Or you may need a line with a more aggressive taper like a nymph line. Or you may need a faster action rod.
You don't want to do a lot of false casting. What I try to do is a pick up, one back cast, and then delivery with a haul. Don't use a leader longer than 9' and in shallow water I would use a shorter leader. With split shot don't try to make too long of a cast. 25 to 40 feet is plenty. Remember that with weight on the fly or with heavy split shot you can make shorter cast and still get a good load on the rod. My preference in rods for this type of fishing is a fast action rod that is 9'6".
Can you tell us about your setup?