As a surf coach and a former contest guy, I had the joys of analyzing a lot of surfers. The good ones had a solid base so it was matter of making tiny changes. For surfers on the opposite end of the spectrum, the changes are easier to find and to work on because the problems are obvious.
But let us say that you came to me and you are fairly new to surfing or just not doing as great as what you would want. For me, I would just head straight to ground zero and fix the problem that pretty much either makes you the good guy at your beach or a surfer stuck in a stink bug stance that people are shaking their fists at because you blew a good wave. And the answer lies in the last sentence.
Analyzing my Photo
In this photo, I am doing a slide off the top so at this point I am not trying to involve the rails. For our purposes, it is great because it illustrates what beginners can not do.
So looking from my waist to my ankles, you can see that my front leg and back leg are doing two completely different things. My back leg to my back knee are cocked forward while my front knee is more stable. They are unequal. If they were both in the same balanced stance, I would not be able to turn very well at all.
There is where most surf school instructors doom their students to a life of stink bug mayhem. They fail to enforce it in new students to ride with their weight on one leg or the other and the majority of the time it should be your back foot.
In fact, if you are having issues and you have just read my post, go out for a surf and catch some waves. Once you stand up, keep bending your back knee and putting weight on your back foot and lighten up on your front leg and see what happens.
And the final analysis of my photo is my upper body. You should be upright and not folding forward at your waist. This does nothing for your ability to turn because if you want to surf well, you need to turn to the opposite direction as well and that requires you to roll your board onto the outside rail.
So work on this and see if your surfing improves.
And I will gladly answer any questions related to improving performance issues!