The first thing you need to do is to figure out how much you know. You need to know which level you are at.
I recommend going to someplace like khanacademy and try some of the exercises.
Another thing I like to do is to find something that I want to learn, that at the moment is over my head. Then I figure out, what do I need to know to understand this? Then I can make a list for myself of concepts/techniques I need to learn.