Their is no quick easy answer to your question. Its takes A LOT of hard work, study, and effort. Hopefully this helps in some way.
Middlegame Planning
- Expand your position:
- Gain more space.
- Improve the position of your pieces.
Decide on what side of the board to play.
- Queenside: a-c files.
- Center: d-e files.
- Kingside: f-h files.
Compare, space, material, and weaknesses.
- DO NOT HURRY. Regroup your pieces, and be patient.
Oftentimes, usually in the early mid-game, if there are no completely obvious or clearly strong moves, and there are many possibilities that look ok (ie. not immediately nor apparently bad), I try to think of some kind of plan. What is my goal here? Is there something I should be aiming for in the long run? Is there a piece of mine that doesn't seem to be doing much, and could be better positioned? (For example, "hmm, this knight isn't doing much here. It can't really move much, most of its movements being completely restricted, it's not really protecting anything, nor threatening anything. Maybe I could find a better position for it where it's more active and has a stronger role, and slowly try to reposition it there?") Does my opponent have a weak piece, like a weak pawn, that I should start putting pressure on?
Most of the time, though, I can't really think of anything, so I simply make a move that "doesn't look bad", and just see how the game progresses eventually. A bit like a waiting move, or a move that maybe advances my position just a tiny bit, but doesn't really have any particular plan or goal.
Should one always have a plan? An actual reason for every move (other than eg "protect this piece" or other obvious urgent moves)?