given you have a good idea of where highlights in hair should be and where you should place your shadows i don't think you're hopeless. The only suggestion i can give you is to keep on experimenting with body shapes, there are several ways to make a body look realistic. And most important of all, when you're done with a skin you have to look at every single aspect of it and check if you can try something different/improve a part. EXPERIMENT (imagine some science lab blowing up in the background to make the statement sound powerful)