How to improve?

Good evening...
I am starting this topic in despair after an almost embarrasing Open Tournament in my city. Still 2 rounds to go, but i know i did  not go well.
I started playing officially at the age of 22 and my first FIDE rating was 1770 without studying at all. Just by watching, playing etc.
After 12 years, 34 now, my rating is around 1500 and I start losing rather easily.
During the game I see that I'm not so disciplined and I may make a few mistakes just by playing fast.
I know that the best way to improve is study but I am completely lost about what to study first!
I want to improve my calculation for sure, but i want to improve my plan creating ability.
Any ideas on how to improve? Please help... 

How much do you play? You havent played here.

I play to another site, I am new to this one.
I play average 1 hour a day, but I prefer tournament chess, not online if you ask me.

Your fide rating would be not the one that you receive after 5 games or so, but the one who you end with after 30 games after your first draw or a win vs rated player.

So your 1770 was probably not very accurate.

For your question - start from the scratch. learn A B C. Start at absolutely beginner level and fill all the holes you have in theory. For example i know it sounds boring, slow and not very helpfull in short run, but why don't you re-learn king and rook checkmate. When i was 1500 i actually did not know the fastest and cleanest way to do it. If you are serious about it , you have to go through all that. Is not hard and you can master it very quick.

Search forums here it has 100 pages with how to improve etc.

Practice tactics - thats the fastest way to improve.

The standard mates such as R&K vs K and Q&K vs K I have mastered at a very quick level. I can also mate with knight and bishop only.
But I think I have a problem in creativity... 

 If someone can barely play a scale on a musical instrument they may also have a problem with creativity... but even if this person were very creative, if all they can do is barely play a scale it wont be relevant.

Learning all the fundamentals and trying to follow them the best you can in your games is what helps for now. You can't reliably find the exceptions until you understand the rules so to speak.

It can get harder the older you get. Just because of the responsibilities of life. Thats not to say you can't improve. Do all the tactics you can. If you know the basics, like general opening principles, what about mate pattern recognition. There are lots of them. Do you know basic end games ? You may have at one time, but don't remember them all, do a refresher course on them, go back over your basic mates as well, over time you can forget them.

what type of openings do you like, closed, open, or semi-open ? Practice your weaker ones. In your own opinion, what are your biggest weaknesses ? Practice on them. If calculation is weak, do numerous tactics, and study common middle, end game positions. What openings do you generally play, for white, and black. Study where you went wrong, do computer analysis on the games, to see where improvements might be also. You might want to get a good book also do a forum search, to find out the most helpful ones for you. Good luck.

Your overall goal is to improve, if you never studied, and just watched, and playing was it, you may find it overwhelming at first. Simply because at the beginning, the more you know, the more you realize you don't know, lol. Take it in steps. Your over all plan should also be taken in steps, of the different phases of the game. 

Opening plans. Good piece developement, King safety. Control of the center. 

Middle game plans. Pawn structure, piece coordination, king saftey. Strong and weak squares. Outposts. Pawn breaks, simplification opportunities when it would lead to a favorable end game position for you.

End game plans. Simplification, queening, pawn promotions. Checkmating.

These are some of the basic ideas in the the three phases of a general chess game. Being good at tactics, knowing pawn structures, and pattern recognition, especially mating patterns, and end game knowledge is also helpful in all phases.

The deeper your knowledge is. The easier it will be for you to make plans.