You would also likely benefit from scheduling review of stuff you already understand with tools like Anki.
Beyond how to study any one thing, the most important thing is studying the right things in the right order starting at a level that is perhaps too easy so as to make sure your foundation is strong and not the source of your difficulties. You can more or less recreate this on your own through online resources and following along typical undergraduate mathematics curricula. There are often dedicated problem books with solutions for most common subjects even at the advanced undergraduate level.
Places to start would be Barbara Oakley's Learning How to Learn and Cal Newport's Study Hacks blog, which has actionable advice like the following: http://calnewport.com/blog/2008/11/25/case-study-how-i-got-t...
You would also likely benefit from scheduling review of stuff you already understand with tools like Anki.
Beyond how to study any one thing, the most important thing is studying the right things in the right order starting at a level that is perhaps too easy so as to make sure your foundation is strong and not the source of your difficulties. You can more or less recreate this on your own through online resources and following along typical undergraduate mathematics curricula. There are often dedicated problem books with solutions for most common subjects even at the advanced undergraduate level.