Getting oriented

The outside before the inside.

Start at the edges

Find the entry points: the main function, the routes, the event handlers. Then follow one path inwards. You always know why you are looking at a file.

README, tests and configuration describe intent faster than source does.
The directory structure is usually the author's mental model.

Run it

Running the code with a debugger or a few print statements answers in seconds what static reading takes an hour to guess.