Proper braking technique braking is probably the easiest thing for most people to improve upon and make a large difference in their driving and lap times. The first area most people work on is  proper application speed and amplitude followed by learning to trail off the brakes and carry more speed into corners. 

One spot to pay attention to is the consistency of how the brake pressure is bled off and how smooth this release of brake pressure is. This first graph shows a good release and a release that could use some work. It's important to work on the skill of keeping consistent and smooth brake pressure throughout the release, especially when blipping the throttle in heal and toe downshifts.