Don’t fall behind your readings. Get a planner and make notes for due assignments, readings, papers, tests, etc. If there’s a week where all your midterms pile up, plan ahead and start studying earlier! Another thing to do is to look over your notes from the previous day before your next lecture. It doesn’t have to be intense, but just something to remind yourself of what you’ve already learned, which will probably make it a bit easier when studying for an exam later down the road.
Get started on your papers early. Try to break down the paper writing - maybe for a couple days you look up sources, and then finalize your thesis the next, then write out your outline, then rough draft, then final edits. If your class doesn’t require rough drafts or outlines by a certain date, maybe try setting a personal deadline for when you want to finish a rough draft so you at least have something on paper.
For physics, I absolutely recommend reading your assigned reading before lecture and paying close attention to example problems in your textbook, specifically the strategy they use to solve the problem. Physics is all about breaking down a problem to its most basic form and working methodically from there, and physics textbooks generally do a good job of walking you through the process. I’ve never considered myself to have any particular affinity for physics, but I ended up doing very well in my physics classes because I really drilled myself to approach problems in that logical and methodical way. And of course, never be afraid to ask for help from TAs or tutoring centers.
Good luck, I also took 18 credits my second semester of freshmen year, so I’ve been in your shoes!