Besides Khan Academy (which is excellent) and other online resources, I would buy text books, and then do everything in the textbook. I mean everything. Read everything in the chapter, work through every example problem, do every practice exercise. Do not skip ahead, or assume you understand without actually doing. And find someone who can answer your questions. I don't like asking for help, but that's held me back. If you have to, pay someone.

I prefer hardbound textbooks, because computers are a big source of distraction. But there are also lots of generally very good free and open-source textbooks you can find online.