A is for asymmetry. Look out for odd shapes, unlike round or oval. 
B is for border. Look out for uneven, or notched borders. 
C is for color. Look out for multiple colors. 
D is for diameter. Look out for a diameter larger than a pencil eraser. 
E is for evolving. Look out for changes in size, shape, color, or symptoms like bleeding or itching. 
Remember the ABCDE's of melanoma to protect your skin.