Opening
Develop your pieces
Move as few pawns as you can
Development is over when Rooks are ' connected '
Middlegame
Use your pieces
tactics when you can - pins, forks and skewers
Checkmating attacks - many pieces
only capture when it gives you some advantage - in space, time or material
Endgame
few pieces - sometimes very few
main aim usually is the fight to promote a pawn
Pawn = 1
Knight = 3
Bishop = 3
2 Bishops = 7
Rook = 5
Queen = 9
King = no limit = game = infinity
roughly - position changes all