Trying to spot a skin cancer on your body can be difficult, because it depends on the type of cell that formed the skin cancer in the first place. If it were a melanocyte which is the pigment making cell, you should be looking for dark spots, multiples spots, spots that seem to be growing in one direction whereas if it's a keratinocyte forming the skin cancer, you should look at sun exposed area. Examine your eyelids, examine your nose, your ears. If you see a bump that doesn't look like anything else, if it's red, if there are blood vessel growing on the bump, if it feels really rough and scaly, it could be a concern for skin cancer.
It's important to know though, precancerous lesions may look very similar to skin cancer, and in most cases, a cancer is preceded by a long period of time of a spot that is actually precancerous and easily treated. The best way to find out whether you have a precancerous lesion or a cancerous lesion is to see a dermatologist. A dermatologist can perform a very simple skin biopsy to be analyzed under the microscope, that can tell you definitively, whether it's precancerous or cancerous.