If most of your casts puts the fly to the left of where you wanted it, assuming you are right handed, it may be because you are not making the rod travel in a straight back and straight forward cast. It is hard for me to explain what I mean but,.....I have seen a lot of people who "swing" the rod back and forward. In other words, they turn their wrist back on the back cast and then turn their wrist forward on the forward cast. A lot like turning a screw driver left and right a little. This puts the cast in a small arch instead of a straight line to the target. Just a thought that was not explained well enough I am sure..........