Every face, scar or no scar, is sporting a top layer of dead skin cells. This is how our skin continually renews itself to look healthy and bright, through cell turnover -- as long as you regularly remove all the dead stuff.
Exfoliating is an important first step in makeup application, and when you're dealing with a scar, it's even more so. Scars can look and feel especially dry and thickened, which makes for a difficult makeup base. Any coverage you apply will absorb better, look smoother and hold longer if you use a gentle scrub before you start.
You can use an exfoliating cleanser with just a small amount of grit (not too harsh!) or an after-cleansing exfoliating cream. One with lactic acid is gentle yet effective.
Done exfoliating? Next secret: You're not ready to apply your makeup yet.