The three fundamental principles of opening play are: control the center (especially the d4, d5, e4, e5 squares), develop pieces to active squares quickly, and castle to ensure king safety. Neglecting any of these principles typically leads to a disadvantageous position.
Chess openings have been studied extensively for centuries, resulting in a vast body of theory with names for specific move sequences (like the Sicilian Defense, Ruy López, or Queen's Gambit). While memorizing opening theory can be helpful, understanding the underlying principles is more important, especially for developing players.
Modern opening preparation at the top level involves extensive use of chess engines and databases. Professional players prepare specific variations with computer assistance and memorize long sequences of moves. For amateur players, focusing on understanding opening principles, choosing a manageable repertoire, and learning the typical middlegame plans arising from their openings is a more productive approach.