READ THE MANUAL!
I can’t overstate how useful reading the manual can be. Maybe a lot of it is stuff you already know (most cameras operate in a pretty similar manner, and most manuals include a quick primer on the basics of getting a good exposure), but a many cameras have their own set of oddities or unique features.
The biggest reason I say this is because I’ve come across a number of cameras who’s previous owners listed them as “broken”, when they were fully functional. A lot of cameras, especially those with electronics, have certain lock up conditions that you won’t know how to get out of unless you’ve read the manual.
For example, the Olympus OM-2 line of cameras will lock up with the mirror up, winder stuck, and shutter button not working when they don’t have batteries or when their batteries die. Getting out of this is really easy, you just rotate the speed dial to B (the bulb mode is completely mechanical), and the shutter will fire and the mirror will flip down. Sometimes this isn’t the case, and they actually are broken, but it seems more common to me that they’re just out of juice.
Another example, for cameras with interchangeable film backs (specifically the Mamiya RB76, because it’s the one I have experience with) will prevent you from firing the shutter if you’ve left the dark slide in the back. It can seem like it’s a dead brick, but really you just need to remove the small metal sheet that prevents light from hitting your film.
If you bought your camera secondhand, and it didn’t come with a manual, you can find copies online available for download. Mike Butkus has compiled a huge number of old camera manuals in his Camera Manual Library, and makes them freely available for download. I’ve never encountered a camera he didn’t have a manual for, but ff he doesn’t have one, most of the time just googling “<camera model> manual” should be enough to find it.