- read the readme
- find out what the usual dev environment setup process is and follow it
- update whatever documentation was out of date in the previous steps ;) no really, there's always something and the noob is the one who will find it. This is part of the assignment we give all new starters - be our "fresh eyes".
- check out the source and have a look through the raw code - is it tidy? is it logical? is it monolithic or broken up? how easy is it to understand?
- pick up some bugs or do a bugfix rotation - this will push you into a random grab bag of code that isn't working but is important enough to have been scheduled.
Since I'm a frontend dev I'll also do an in-browser evaluation of the code, run some validation checks, performance checks, etc. That's probably not what you're getting at though.