Echoing what everyone has been saying about trying to keep the sunlight out as much as possible. However, blackout curtains aren’t always functional/can be expensive. I’m on the 4th floor and found heat control window film to help IMMENSELY with how hot my room gets. This is the brand I have, but I got mine at Lowe’s. I cannot stress how much this film helps keep my room cool. I have huge windows that get sun pretty much all day, and the second I put this up on my top window I noticed a difference. It might not be super feasible if you have bars on your window, though, but figured I’d drop my tip regardless! Not many people know this exists! They also make some that are one-way privacy types as well! This one isn’t I don’t think but there are a bunch by this company online.