So, focusing on the "how do I get to be a better diver"....
Good advice above. No substitute for lots of diving and learning from other divers. You'll never stop learning.
In terms of things I would advise a brand new diver to focus on in order to improve:
1. Buoyancy. The ability to comfortably control your depth and remain neutral is the single most important skill to develop. It's a safety issue, obviously. But also, good buoyancy skills will significantly reduce your gas consumption, give you much greater comfort and free you up to enjoy the dive. Much like riding a bike: when you first learn, you spend the whole time just trying not to fall off, but soon it becomes natural and you can actually start to look around and enjoy the ride. So, getting to the point that buoyancy control is natural and subconscious is a key goal.
Without getting into details that take us off track, figure out how much weight you really need (many OW students are purposefully overweighted for class) and as you get more comfortable you'll almost certainly need less weight. Unnecessary weight complicates everything. Work on learning to hover at a constant depth without sculling or finning and get used to the effect of your breathing on your buoyancy. Stop moving entirely and see if you start sinking or floating, then get neutral and then learn what it feels like to swim that way. This will become second nature before you know it, but if you can focus on this as a priority for your development now, it will come much faster.
2. Keep notes, in your log or otherwise, after every dive about what you feel you could have done better, or if you are having some gear issue. When I started out, and every time thereafter that I changed configurations, I made a point of trying to identify the one, two or three things that really bothered me most about a dive or series of dives, and then fix it for the next time either through practice or tweaking the setup.
Eventually, as you fix things one by one, you'll find that there's either nothing left, or what is left is really trivial. Especially in the beginning, it is an iterative process.
3. That said, measure twice and cut once. Don't go crazy on buying gimmicky gear, for example. There is tons of garbage out there, or at least stuff that is not generally necessary. Focus on gaining some experience and nailing down the fundamentals. There's tons of good information out there generally, and on this board specifically. But, you''ll have to learn to judge for yourself and separate the wheat from the chaff and only experience will let you do that.
4. To your comment about challenging yourself. That doesn't have to, and shouldn't, involve risk or "raising the stakes." At this stage, you will learn far more in the first 30 feet of water, where buoyancy control is more challenging, than on deeper dives.
Challenge can be learning to do all those skills you're practicing mid-water, rather than on a platform, seeing if you can learn to hover in place for minutes at a time, nailing your buoyancy so you're not carrying one extra pound of lead, learning to use a compass underwater and follow a course to find the next point of interest in the quarry, teaching yourself how to frog kick rather than flutter kick, or how do a helicopter turn. Take an extra 2 or 3 lb weight (more later) with you and put in on the platform. Figure out how to pick it up, swim the edge of the platform and put it down while staying neutrally buoyant. Practice holding safety stops without having to grab the line, etc. Those are the challenges that will make you a better diver right now.
