Honestly, what's worked best for me is buying a book on the topic I'm interested in, and just working through it methodologically. The most difficult thing has

Honestly, what's worked best for me is buying a book on the topic I'm interested in, and just working through it methodologically. The most difficult thing has been checking my work since answer manuals are difficult to come by. If I'm really unsure, I'll try and find an appropriate group to post a question to. I'm mostly interested in algebra, category theory, and topology, so it's difficult to just ask a computer to check my work for me.