[wpm]

I've found for me what helps me do such things is actually writing, but writing about what I read. It forces me to not gloss over or skip anything. Like a form of recital. "This function takes a pointer called blah and uses it to blah blah...". I'll go line by line basically rewriting the program in plain English. Especially helpful for languages I'm not that familiar with.

As someone mostly self taught that's how I've always done it until I do it enough I can do it in my head.