Development is one of the three fundamental opening principles alongside center control and king safety. Each piece that remains on its starting square is essentially out of the game, contributing nothing to attack or defense. The goal of development is to bring all pieces into active play as quickly and efficiently as possible.
Key development guidelines include: develop knights before bishops (knights have fewer good squares and benefit from early positioning), avoid moving the same piece twice in the opening, develop toward the center, connect the rooks by castling and clearing the back rank, and avoid early queen excursions that can lose tempo when the queen is attacked.
A lead in development is a temporary advantage that must be exploited quickly before the opponent catches up. Opening the position (through pawn exchanges) when you have a development lead is often the best strategy, as it creates opportunities for your active pieces. Keeping the position closed when behind in development helps neutralize the opponent's advantage.