It took me three years of the same three working sets, every single session, before I noticed I'd been reading them in the wrong order the whole time. Once I actually saw it, the fix took about a week to change how I trained.
Your first day
Start by picking one exercise and a genuinely light weight. If you're not sure where to begin, a plain barbell (45 pounds) works for something like a bench press, and a 15 or 20 pound dumbbell works for curls. Going lighter than feels necessary is fine here. You don't yet have the control to safely handle what you might actually be capable of, and starting light protects your form while that control develops.
Do a first set aiming for 8 to 10 reps, with real form, no swaying or momentum (a quick video or reference guide can help you check this if you're not sure). Count exactly how many you complete before you can't finish another one cleanly. Rest two minutes, then do a second set the same way, and a third after another two-minute rest.
The whole thing, start to finish, takes about six minutes. What matters most happens in that first set: clear more than ten reps on it, and that's your signal to add weight next time. Come in under eight, and it's time to drop the weight instead. It's fine if the second and third sets dip below range, as long as the first set landed inside it and the drop-off isn't dramatic. If you're attempting something riskier like a heavy bench or squat, use a spotter until you're confident.
The thing most people miss
For years I let my second and third sets decide things. If they eventually landed in range, that felt like proof the weight was right, even when my first set had already cleared the top of it with room to spare. I had it backward. My first set is the one I do fresh, before fatigue from the earlier sets has a chance to build, which is exactly why it turned out to be the set that actually meant something.
Once I flipped that, my progress moved faster. My incline dumbbell press went from 60s to 75s in a few months without a bulk, and other lifts moved the same way. Waiting for every set to feel consistent before adjusting weight had quietly cost me months of strength I could already have built.
What not to buy
You don't need much starting out. A few sets of weights and something to sit or lie on cover the first several months of this completely, and a home gym or a public gym almost always already has a full range of both. I never needed anything beyond that early on. The equipment was never what slowed me down.
Knowing when to add weight was never the whole picture, just the piece I got wrong the longest. There's still programs to plan, nutrition to get right, and form to keep honest under real load, on top of knowing when to actually push the weight up, and I'm still working through all of it. None of that means much, though, if you're still guessing at the number itself. Fix that first.