Don't pick or pop! Don't pick or pop pimples. That can cause scarring. If you get deep, painful pimples, see a healthcare provider. Those are the type that tend to scar.
Avoid Sqeezing! Picking and squeezing almost always leads to scarring. Though popping a pimple may make it less noticeable temporarily, you can cause it to stay around longer. By squeezing pimples, you actually push bacteria further into the skin, increasing swelling and redness. In fact, more damage can be done to the skin by picking and squeezing than by the acne process itself. Instead see your dermatologist!