[ricardolopes]

I like to focus on the main business element. If it's a SaaS for sharing videos with comments, for instance, I'd take a longer look at the video and comment models, their relations, and the call chain from API endpoint to model.

Another strategy I like is picking parts of the codebase and trying to refactor them. You don't even need to commit anything if you're not supposed to go around changing things: just by spending some time moving things around, seeing what breaks and so on will give you a better understanding of the code and what it does.