1. Show up to office hours. Even if you sit there and do nothing, TA's notice -- and TAs will absolutely spill the beans on what to prep for for exams, even unintentionally.
2. If you're so brainfried that you can't study any more, go to the gym. Not only is exercise generally good, I'm real convinced it's good for memory consolidation too.
3. If you're attending an expensive private university, networking is effectively what you're buying. Exploit ruthlessly.
This is how I got into my job. It's never too late. Bring yourself out and talk to people.
my first graduate school advisor took me on as a full staff member 5 years out of undergrad. It turns out he knew exactly who i was and was keeping tabs on me in industry, waiting for me to reenter the market. I don't know what I did to deserve that, but I'm eternally grateful.
Even if it's not an expensive school, email / talk to all your professors, classmates, lab partners, etc. I didn't start doing that until my 3rd year.
For me it was: My mentor's friend -> internship -> first job
Just showing up and hanging out in the TA's office when you don't have any question seems kind of weird to me.
I read a study a while back that showed taking breaks after learning/studying is crucial to efficient memory consolidation. Breaks can be filled with other activities, like working out. Promoting general blood flow, prob doesn't hurt in getting fresh O2 to the brain while it's doing it's thing....