Ways to read source code and learn?

I've been reading through source code for various programs to get better at programming. I know that many of the people here also do this.

I'm wondering what your approach is when you're trying to learn from source code (not debug, but reading it to get better at programming). Do you go line by line, follow a top-level function call, etc? Also, if you're familiar with the syntax, do you quickly skim over boilerplate code to be more efficient?

Thanks for any advice. Trying to speed up my learning process.