As a preface, I was bored at work so I started jotting down everything that came to mind. I hope it makes sense. I don't know the OP's playing level so I've kind of generalized. This doesn't obviously encompass everything, as each point could easily be expanded upon into a book in of itself. I hope this helps.
First of all, the phrase "good enough" can never be uttered. You need to be striving for perfection during practice as much as possible. Perhaps you can leave a certain area of practice for another time, but you need to endeavour to improve upon it during your next outing. You need to practice you're weaknesses, but do not forget your strengths either. I find it is a misleading piece of advice to not practice your strengths, remember what one person considers to be a good shotmaker, is a weak one relatively speaking to better players.
Even your best performances need to be analyzed for a way to improve. If you have a night where you run 6 out 7 racks, why didn't you run the 7th? If it was due to a mistake, practice it!
I feel very strongly that you need to split between practice and competition roughly 60/40. 60% practice, 40% competition. So my recommendation would be to play only one league and use the time from the other to add to your practice regimin even if it is practice matches or gambling with stronger competition.
You need to be continually playing up in skill level in my opinion. One of my issues with leagues especially ones where there are few or no A level players, it's easy to get stuck in a rut. People tend to have very negative attitudes towards improving/obtaining higher handicaps, they often act as though it's absolutely impossible or that you need to be supremely talented. It's amazing how being surrounded by naysayers can affect ones confidence. Playing amongst top players not only gives you a bar to reach for, but it shows you it IS possible should you be so inclined to work hard enough.
In your practice you need to be a perfectionist of almost obsessive compulsive levels. As a general rule, any shot within roughly 4 feet and a 0-50 degree angle can not be missed. And eventually you'll need to expand you're unmissable shots beyond that. I view improving at pool as a process of adding more and more unmissable shots to your repetoire. This means becoming comfortable each potting angle wherein you can play it with any speed and spin without concern of missing. This is expanded even further to specific positional routes that you can make consistency. Don't get me wrong though, every player will miss any shot of any difficulty at times.
If you miss a shot or position in practice, set it up and try it again. Absolutely do not leave it unless it was a difficult shot that anyone will miss most of the time (but those need to be practiced too!). If you set it up and play it again, not only will you begin to learn how to play it, but it affects your confidence. Seeing yourself make the ball and obtain position will give you the confidence you need during your match. Alternatively if you don't practice these misses, the shot may come up 4 times per session and you miss it all 4 times, or even 3 times, how confident will you be when it comes up in a match?
Position play however is the key to being a run out player. It doesn't matter how good of a potter you are, no one can pot them from the lampshades forever. Pros and top amateurs play positional routes that give them the most room for error. Many mid level amateurs on the other hand play positional routes wherein they need to place the cue ball on a dime (generally due to either a lack of knowledge or an increased focus on potting the ball). So take note of how pros approach shots and practice it. Safety play is similar wherein top players generally try to play a safety that gives them the most room for error.
All that said, you can't break and run that many racks without a solid break (my weakest point). Your biggest focus of course needs to be a solid hit on the cueball and a solid hit on the head ball, even if it means hitting the break with only 50-60% power. No point in throwing you're body into it if you hit the ball sloppy. I find that if I warm up hitting the break soft, slowly I'll get into a gear wherein I can ratchet the break up to 80% power.
In order to achieve all of this, you need solid fundamentals. They may be the "basics", but it is something you will need to focus on during the entirety of you're playing career. Strong mechanics are what breed consistency. Focus on your alignment, solid stance and perfect your stroke. Stroke timing is everything, it allows you to generate maximum amount of power with minimum effort, which leads to a more accurate stroke meaning fewer misses and better position.
Last but most certainly not least....practice absolutely every major game you can. Even if you don't compete at it. In my area people play 9 ball, 8 ball and snooker but I practice far more than that. Every game is, imo, a drill in of itself. Snooker improves you're mechanics, 9 ball improves you shotmaking on the pool table and playing multi rail positional shots, one pocket trains you to get on the right side of the ball (it's great for safeties and banks too). Straight Pool will help with everything, consistency, shotmaking, position play, breaking clusters etc. If you can get on to a carom billiard table, that will definitely help you're kicking and position play. You need to know the exact path of the cue ball, not a general idea. Personally, I'm working on English Billiards at the moment.
That's all I can think of at the moment. But, in short, it needs to be a passion. And you need to obsess over it (healthily of course). I think anyone can be an A player, but not neccessarily a pro. You don't need to devote your ENTIRE life to it, but you do need to prioritize your time to figure out how to squeeze every ounce of practice in with out jeopardizing what is truly important. And try to remember, it's a game and if you're not having fun, there's really no point in playing.
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