In a race I tend to follow (or Push the guy in front of me, without touching them), let the other guy mess up...I just make sure, too, that I'm there at the end. Alot of guys drive super hard and hit something or someone and put themselves out. I run at 80% for 80% of the race then start really concentrating on where I'm placing the car and running harder. After 15 minites of a 20 min main, you've got the car felt out and know what its going to do at every corner.
At the track, in practice, I pick a corner, and try to run it as fast as I can, nail it, close and fast...then I move on to the next corner and concentrate on it..etc. Take the track apart and learn it fast, in segments. Ever notice how some corners you can have the nose pointed RIGHT at the apex and it slides right by? You can't take those corners fast without practice at them...and so many times slow is faster, than (trying) really fast and missing the apex or turn....The best heat or lap can feel like its slow.