Positional Assessment and Strategical Planning Approach
This is an approach I learned years ago when I first started playing chess more seriously. (The original source was a book by GM Oleg Chebotarev.)
As soon as you get out of the opening, and as needed subsequently, it's important to ask yourself the following questions:
* Who controls the central squares (e4, d4, e5, d5)? For which ones is there shared control and for which ones is the control by one side only? Is the center mobile or is it fixed / closed?
* How well developed are the pieces of each side? Are the pieces active where they are currently positioned (or are they merely moved out of their original squares but not on "active duty" yet)?
* How safe are the kings? Yours and the opponent's?
* How are the heavy pieces positioned (yours compared to those of the opponent) -- symmetrically or not? Which group is more active given the other nuances of the position?
* Are there open or semi-open files? If so, who controls and can make better use of them?
* Are there open diagonals? If so, who controls them?
* Which squares are weak in the position of each side? (This may include squares that are currently occupied by a piece, e.g., a pawn, or squares that are empty but undefended.) Which squares are strong for each side? Is there any obvious geometry (alignment) between the weak squares of your opponent and strong aspects of your position? What about geometry that is present in your weak squares that your opponent might take advantage of?
* On how many of the above questions the assessment of the opponent's position was better than the assessment of your own position? On how many was your position superior? The balance indicates roughly who might have an advantage and where specifically...
Answering those questions clarifies:
* Who has an advantage, or perhaps whether the position is equal?
* Where is that advantage? E.g., development, control of open files or diagonals, strong/weak squares, unsafe kings, etc.
* How might that advantage be exploited (if it's yours) or minimized (if it's the opponent's)? Examples of this are many:
** hindering the opponent from developing their pieces well and improving the placement of their already developed pieces, including by constantly posing threats that increase your potential and do not help the opponent catch up since they must respond to those direct threats;
** starting an attack if the opponent is undeveloped or if their king is unsafe;
** increasing pressure on open files/diagonals that you control or decreasing the pressure on those that your opponent owns;
** preventing the opponent from transforming their weaker squares into stronger ones;
** taking maximum advantage of your strong squares and the opponents' weak squares by pressing the opponent on them, including by exchanging pieces that would further highlight those weaknesses in their camp;
** minimizing any targetted attacks at your weak squares, including by exchanging opponent's pieces that can attack them;
** exchanging the opponents' active pieces as a way to reduce their pressure;
** exchanging your passive pieces or maneuvering to improve their placement as a way to improve their utility;