Nice to see you got out there!
You'd probably be well served to practice shifting in an open, low-consequence setting. A big, grassy field with a gradual hill is helpful. Get a feel for which lever makes it "easier" and which makes it "harder" and also start to get a feel for timing. Downshift too early, and you'll find that there's a period of time where your pedaling doesn't help at all. Shift too late, and you'll hear a nice "crunch" as the chain attempts to move. Don't do that. It'll take time to work out when the "best" time to shift is, but I like to do it when I feel the extra resistance from the climb, but it's not "too much" yet. And then try to only do one downshift at a time at first. You can really get into trouble by trying to dump a whole bunch of gears at once when you're pushing the pedals. You can pull it off, but it requires that you have enough forward momentum that you can "soft pedal" a couple strokes while the chain completes the shift. As you get to know the trails, you'll start to improve your timing.
Riding over obstacles is going to require some extra skills. Just letting the bike roll over stuff is going to really test your ability to keep it under control, especially without suspension. You need to work on moving your body weight around over the bike. You can look up some drills for this on youtube, and parking lots are good spots for this practice. As you get a feel for where you can move your body, and being comfortable doing it, you'll be able to start working on USING shifts in your body to get the wheels off the ground to make riding over stuff a LOT more smooth. The less suspension your bike has, the more you need to use your body for this. I'm getting some good lessons on this since I started riding a hardtail again for the first time in about 18yrs. I'm having a lot of fun with it.
Speed is generally your friend on that stuff, but you've gotta work to be able to use it. Like I said, you can't just plow over stuff all the time. Sometimes you can, but working on the range of motion drills and then on to lifting your wheels over things will help you a LOT.
Also, learning to read the trail and see the line you like best, and the control to hit the line you want is something you'll want to work on. Riding with others willing to stop and session stuff can help a lot here. You can talk about the lines you see together, watch others on them, and get feedback when you try them yourself. Sometimes if you just stop and hang out at a technical spot, you can just watch other riders ride through. It can also help if you video record yourself. Set up your phone or other camera on a tripod or have someone else record you. It can help you identify where you went wrong, especially if you can compare to a video of someone riding it successfully.
As for braking, you want to work on using them BOTH. Once you get comfortable with using them both more or less the same, you can start working on giving one brake a little more or a little less force than the other for certain situations. Generally, for trail riding, it's exceedingly rare that you'll ONLY use one or the other. You also want to brake BEFORE the turn. You only have so much traction on your tires. If you're trying to split it between braking AND turning, it's going to be a painful lesson. It's possible to feather your brakes through a turn to help control speed, but I'd call that a little more advanced braking technique. At your stage, it'll be better to avoid braking IN the turn. Brake before it so you can roll through.
It'll be very similar when dealing with technical stuff, too. You want to do your braking (slowing down) before the techy spot. Brake in the middle of it and you're likely going to have to step off the bike in the middle of a bunch of rocks or roots where you run a risk of buggering your ankle or something else (like a collarbone). Most of us have done this at some point or another, though. The art of the bail is a skill all on its own.
Riding gloves are important, but IME don't tend to do much for blisters. The reason I started wearing them in the first place was to keep my palms from getting shredded when I crashed. I don't do that so much anymore, but they're super beneficial for maintaining your grip on the bars when you're sweating balls. I ride in the southeast, and sweat is inescapable in the summertime. Usually I'm swimming in it. If I forget my gloves for a ride, I'm honestly quite terrified my hands will slip, and I ride super conservatively.
