Examine all over. It is important for you to examine your entire body as skin cancer can occur anywhere, not only on areas exposed to the sun. You should be familiar with your birthmarks, blemishes, and moles so you know what they look like and can spot changes. As you examine your skin, look for changes in the size, color, shape, or texture. If you see anything concerning, see a dermatologist!
Look in mirror. Examine your skin regularly. Look for spots which are changing in size or color. Also look for spots bleeding or ulcerating. If you see any, make sure to get them checked out. If you have a strong family history of skin cancer, see a dermatologist early.
Routine skin checks. Routine physician and self skin/mole checks will help detect skin cancers early. The following site from the american academy of dermatology informs you how this is done. http://www.aad.org/skin-conditions/skin-cancer-detection/about-skin-self-exams/how-to-examine-your-skin.
ABCD's. Remember your abcd's when thinking of melanoma. Look for moles with asymmetry boarders that are irregular color differences within the same mole diameter greater than 6mm also any new mole or old that starts to itch, bleed or ulcerate should be of concern. Another rule is the ugly duckling rule. Which refers to a mole that looks distantly different from the others on your body.