A marginal plan, executed well, is better than a brilliant plan executed poorly. I think every experienced competitor started out struggling with stage planning and execution (primarily execution). First course of action should be to identify all the targets that you will need to shoot; I walk down range and around obstacles after reading the stage description to make sure I'm not missing one. Next is to plan where you will shoot those targets from. Usually simple is good, don't try to out-strategize the stage planner until you can reliably execute plans you come up with.
Now comes the hard part. Visualize the entire plan over and over in extreme detail. Each target, each step. See the sights settle at the exact spot you want to shoot on each target, see them lift in recoil and settle on the next target. Repeat this visualization several times. If you have prepared properly, you will simply execute the plan without having to devote conscious thought to it when the time comes. If you can do that, you should be able to get through a stage without it all evaporating on the beep.