I have just started a new job in which I will be overhauling and updating a web-application written in Django. I have a loose familiarity with Django (and have been reading up on the documentation for Django and external libraries like Django REST Framework). But I am hoping someone with lots of experience in quickly understanding existing web applications so they can update them would have some suggestions how how to best do so, both in general and with respect to Django.
What to look for in the code, tutorials to look at, perhaps there are some defined methodologies for understanding old code I can implement.
I realize this is a subjective question, but would appreciate any suggestions, including where to ask this question that might yield the best responses.