.........or those about to start
In my opinion the prospective beekeeper would be well advised to take things steady in the early stages and approach beekeeping in a sensible way. I have seen many instances of people rushing headlong into it before learning anything, then finding out how much work is needed, or they don't like getting stung, and quickly giving up. If you decide to take up golf or cycling and you give it up after a short time there is little harm done, but a colony of bees is a different thing. There are diseases that a colony can easily pick up and if the bees are abandoned they can be a source of infection for other colonies for some time.
All beekeepers develop their own management system and this could be for a number of reasons - their location, the way they were taught, what "seems" the right thing to do, etc. In reality we are probably all slightly different, but that's no problem providing there is enough knowledge to understand why things are sometimes done in a different way.
Beekeeping at a basic level is actually quite simple - it's humans that have made it difficult! It wasn't so long ago that many beekeepers had a few skeps in the garden, but knew very little about what was going on inside the colony. They did much of their beekeeping using observation and logic, but they always had bees and they always had honey. I know we are unable to keep bees in that way now, due to the many problems bees have, but learning the "basics" at an early stage will allow you to deal with much of what you come across during a normal season.
I strongly advise joining a BKA, but please remember they are run by volunteers and vary considerably, depending on their resources and who is there. Some are incredibly good, but others may not be. If you are lucky enough to have a good one, then make use of it and please help out where you can to ease the burden on others. Even the new beekeeper may have skills that nobody else has. If you have a poor BKA, you have a bit of a problem. I don't wish to cause problems at a local BKA, but as a beginner you need to learn quickly and good sound stuff as well. Before deciding on which one to join I suggest you visit all those within a distance you are prepared to travel to on a regular basis and join the one that suits you best. If you are stuck with a poor BKA, you have three options - walk away, stick it out and hope it gets better, or find out what the problems are and do something about it. None of these may appeal to a raw beginner.
Have a chat to everyone, including the quiet ones - it is often them who are the better beekeepers. It won't be until later when you know enough yourself, that you realise the beginner is often seen as fair game by some, who think they know enough to "advise" you or "take you under their wing". The reality is they may not know much more than you and often won't ever know any more, where hopefully you will overtake them quickly.
Much of your learning will be done at your local BKA. They should have a teaching apiary, or at least regular apiary meetings, where the bees are inspected by experienced beekeepers. Keep your eyes open and look for different techniques and different answers to the same question - there will be many. You can often learn as much, or more, by watching someone than listening to others.
Get to meetings as much as you can. Handle a colony as often as you can on your own until you are satisfied you can inspect a colony of bees without help - you will have to at home. Speak to the tutor/demonstrator and ask them for an honest opinion if they think you are ready to have your own bees. Take advice on where you should obtain bees and equipment. Don't buy "blind" such as on the internet, as I have seen some disasters and there is more than one way of getting stung in beekeeping! It is much better to see what you are buying.
If you are unable to keep bees at home, find somewhere to keep them that will be convenient and not a nuisance to anyone else. When you have the opportunity to acquire bees ask your BKA for guidance and if possible for someone to inspect them for disease.
When you have your first colony you should have already acquired enough knowledge to care for them in a responsible manner. I always advise beginners to have two colonies fairly quickly. This is because things can go wrong, terminally sometimes, and if you have a second colony you can help it out without needing to seek help from another beekeeper.
Although you should be reasonably competent at this stage there is a long way to go and a lot to learn. Understand what I call the "basics" as quick as you can, so you can identify the needs of a colony and how to address them.
Continue going to meetings and make sure you are challenged. Push yourself to learn more without being a "pain" to the tutor/demonstrator or other members.