[ohitsdom]

Another vote for "learn the stack".

Also, if you have the contact info of any developer/lead you'll be working with, reach out to them and ask what you can get a jump start familiarizing yourself with. I've had interns do this and it definitely made a noticeable difference. I mostly told them to get familiar with the stack and gave them quality free resources (while stressing it was voluntary). They didn't come in an expert or anything, but it did seem to help their heads from spinning too much during the first day/week.