Pieces developed onto unattacked squares, squares under control (because more attackers than defenders), undefended pieces, a balance of control on the white/black or both, open files, half open files, open diagonals, half open diagnals, pawn structures, doubled pawns, isoated pawns, pawn islands.
It's a nuanced thing, it's also largely how chess engines evaluate a position - it's not something humans can do because to do all of the above would take too long however strong players get an intuitive grasp of all of that and more and use it to assess a position.
Pieces developed onto unattacked squares, squares under control (because more attackers than defenders), undefended pieces, a balance of control on the white/black or both, open files, half open files, open diagonals, half open diagnals, pawn structures, doubled pawns, isoated pawns, pawn islands.
It's a nuanced thing, it's also largely how chess engines evaluate a position - it's not something humans can do because to do all of the above would take too long however strong players get an intuitive grasp of all of that and more and use it to assess a position.