Read the pawn structure first
Pawn structure is the most stable feature of a middlegame position — pieces move, pawns rarely do without commitment. Before calculating specific moves, it's worth asking what the pawn structure suggests: where are the open files likely to appear, which side has a space advantage, and which minor pieces are strong or weak because of where the pawns sit.
Identify your worst-placed piece
A simple, repeatable exercise: find the piece doing the least work on your side of the board, and look for a way to improve it. This single habit generates a surprising number of good middlegame moves, especially in positions without an obvious tactic.
Play on the side where you're stronger
If your pieces and pawns give you more space or activity on one flank, that's usually where your plan should be aimed — trying to force action on the side where your opponent is better organised tends to help them, not you.
Convert an advantage, don't just hold it
A small edge — a better pawn structure, a more active piece, a safer king — needs a plan to become a full point. Simply avoiding mistakes is necessary but rarely sufficient; look for the concrete way your advantage can be increased, whether that's a pawn break, a piece trade that favours you, or an attack on a fixed weakness.