What do skin cancers usually look like?

Non-healing wounds. If you have a growth that is not healing, and tends to bleed on its own, you should definitely bring it to the attention of your dermatologist. For photos of common skin cancers, please see the following website: http://www.Aad.Org/skin-conditions/skin-cancer-detection.
ABCD's. Melanomas are screened by the abcd's: a-asymmetry; b-irregular borders; c-different colors; d-diameber >6mm (size of pencil eraser). If you notice a mole with these characteristics, get it checked out asap. If you have a skin lesion which is growing, ulcerating, bleeding, or otherwise changing, get it seen as well for evaluation and possible biopsy. Best wishes.
Varies. There are several different types of skin cancers. Squamous cell the skin begins as a small nodule and as it enlarges the center becomes necrotic and sloughs and the nodule turns into an ulcer. Basal cell patients present with a shiny, pearly nodule. Melanoma patients have an irregularly appearing pigmented lesion.
Growing sore. Skin cancer often begins as a small bump that looks like a “pimple that doesn’t go away”. It gradually enlarges, and sometimes bleeds. The cancer may appear red, pearly, scaly, flesh-colored, or darker than the surrounding skin. If you have a growing spot that doesn't heal, you should see your dermatologist.