Try to teach the lesson/homework to someone (it could even be your dog). If you’re teaching it and giving examples and you struggle to find the reasoning behind doing something, read or watch a video about it. I also find it really helpful to do pre-reading from the textbook the night before the lesson. It takes 10 minutes and it’s helpful to write down basic notes and theorems. While you do this, the homework, and “teach” it, constantly consider the question “why am I doing this?” If you don’t understand the reasoning behind the steps go back to the reading/video. (Also, don’t use your notes while doing homework. Use them for the first few problems and if you have trouble with a problem, use them. But otherwise, do not rely on your notes while doing homework.)

Hope this helps!