Undergrad to PhD advice?

I’ll be starting a PhD in comms/journalism studies in the fall. I finished undergrad last December and have been doing some long-distance hiking and other adventurey stuff since then.

I’m wondering if anyone else who went straight from undergrad to a PhD program, especially in the social sciences/humanities, has any general advice. Things to do? Things to avoid doing? Pointers on successfully making the shift? Things you wish you knew? Thanks in advance.