Steps of improving

Experience Elubas... experience...

Once you know the basics, it's just a matter of time before you begin to grasp positional concepts and all of that other stuff, simply from playing.

Well by basics, I mean also after the beginner stage, like the kind of stuff you learn from how to reasses your chess or the amateur's mind. And for tactics, studying them is a much better way to improve than simply playing. Because tactics are easy to practice. I would say if you're lucky you'll learn a few positional concepts, but you'll probably have lots of holes in that department and your tactics could also be much better simply by solving puzzles or going over master level miniatures. So yeah, after you know alot by chess, in my case the only step between my current rating and say 2000, is solidifying what I know and put them to use in my own games. Going over my weaknesses and what not, but the moves I make are still based on what I learned.

I understand the virtues of experience, but you have to mix the two. Experience is not going to give you the knowledge you need (for the most part!), it helps you put it to good use. If you really haven't studied to get where you are, i guess that's impressive. But I'm sure it would have been alot easier to study those things first and I doubt people can get to where you are from purely playing, no matter how much. just going over games is not automatically going to give you positional understanding. After you have that understanding, it's just the going over your games that will make your rating very high.

What's your best and worst?

Improve your worst, and use your best :)

I have played in tournaments since 1994, been on the same level for some years, played some good games and some really bad. Why?

In the good games I found the right plan, and in the bad ones, I had none!

The opponents didn't really matter, so I'm working on the planning part.

I see what you are saying.  I do remember a couple years ago getting some chess books at the library and reading through them, but they didn't seem to help as my rating simply plateaued for months.  So I just decided to play a lot of blitz chess against better opponents, and all of a sudden things started to click.  I'm not ultra-awesome at chess or anything, but I feel I have a "decent" understanding of it now, and I think it's all because of experience and mass repetition.

By meaning they didn't help, that doesn't mean you didn't learn anything. it's possible to at first get worse in games after reading books that make you think different, but for me I started to see how to implement what I learned and got much better. The proper serve in tennis is hard at first and by not being so good at it you start doing worse than usual at getting them in. Or maybe a certain way to bowl is easier bu not the best way. But once you get good at it, it will be the best way to go by far, while being good at the improper way is easier at first but limits how much you can improve  You may have done the same. You got out of the plateau by actually getting better at an OTB situation, but could you have done that without learning anything from books or any study?

The only suggestion I would add is not to annotate with a computer.  Too many people rely on computers to show them moves they missed in games, but computer analysis will not point out positional errors, you must find those yourself.  Comp is really only good for finding obscure tactics after the game imo.  Do your own post game on a board without a computer and write out your own variations, it will help your calculation skill also.  Calculate it in your mind, then move the pieces and see if you missed anything.

Computers are good for getting to the bottom of a tactical positions and showing tactical errors but it won't tell you why you're making them and does not at all help with positional mistakes, so a combination between computer and non computer analysis is good.