Just found this thread and only read the first paragraph of Bobs post and started laughing because he is right on the money. Like I said I didn't read the whole thread so forgive me if this has been said.
Pay a couple bucks to the promoter for printouts of your races, go home and study them, put them in a binder and compare week to week track to track.
It will be painfully obvious quickly where you can improve.
Personally if I can't drive within a car width of the line I want I slow down, when I have the car and my brain a little more dialed I'll step it up a bit. Discipline like that will also make you much more comfortable running door to door knowing if the other car misses his line very much you can easily pass.