Tactical indicators

Look for weaknesses and tactical indicators such as weak, undefended or hanging pieces; checks; the strengths of competing pieces such as squares commanded; forks and pins; batteries;passed pawns, unsafe king, weak squares, files and diagonals; pieces with limited mobility.  

A mneumonic for remembering how to assess a position is KMAP: kings' safety, material imbalances, the activity of pieces, and pawn structure

And then calculate, firstly, forced lines or tactics and secondly strategy or fussy logic.

Manouvre for tactical advantage.

Study a position by identifying which squares and pieces ('resources') each piece is attacking or defending.  Do this for your own and your opponent's pieces.