Is there a good method to come out with a plan during a game I started to play chess more serious those days, through playing some tournaments. During all the games on those tournaments I face serious problems coming out with plans during the middle game, is there a methodical way of thinking to come out with a plan, by looking to a given position? Or a good book that I can read to improve this skill?. My current Elo is +1600, I have played around 20 standard time control games.
Its a great question! When teaching chess, I get on my students about always having a plan. However, many of my beginning students have the impression that making a plan means "I'm going to use a combination of Queen and Knight to Checkmate my opponent's King on the 27th move." Of course, this is unrealistic.

Chess is a constantly changing landscape and two or three moves can completely turn a winning position into a losing position. Therefore, plans have to be flexible. That's where it gets tricky. I tend to create flexible plans in which I play elastic moves. Planning really comes into play during the middle game. 

Once the opening is complete and you have your pieces on ideal squares, you get down to the middle game. At the start of the middle game, I go through a checklist included pawn structure, position of my opponent's King in relation to his or her defending pieces, material balance, etc.

If I'm down material, I create a plan that evens the material balance which repositioning my pieces on good squares. I try to keep it simple and flexible. I think a lot of players have narror plans and when something goes wrong, they find their pieces on squares that do them no good. I try to play elastic moves that prepare for more than one response from my opponent.

My plans change as the game changes. However, I try to play positions that allow me to maintain my original plan while still dealing with the potential curve-balls some times thrown by my opponent.

It's a tough call because you want to have a plan that goes forward but often you have to rethink your plan and alter it to fit the current position. I would say that your plan has to take into consideration imbalances but that is often the cause of a change in plans. A master can see many more moves ahead than I can so it is easier for them to create a plan that they can stick to. Moreover, Andrew Martin has mentioned on numerous occasions the need for playing flexible moves.