Opening principles every player should know.
GM Artur Yusupov from 'Build Up Your Chess' :
''The first principle of opening play is rapid development of all the pieces.''
''The second principle of opening play is to struggle for the centre.''
''The third principle of opening play is to struggle against our opponent's ideas, in order to make his development more difficult and to prevent him from achieving control over the centre.''

Chess Openings Resources for Beginners and Beyond...
https://www.chess.com/blog/RussBell/openings-resources-for-beginners-and-beyond