At some point in every strong chessplayer's career, he stopped and made a deliberate study of tactics. A skilled tactical player can reach the Class "A" or even expert level with only limited opening or endgame knowledge. No amount of opening or endgame study, on the other hand, can make a good Chessplayer out of a weak tactician.
How does one improve tactically? The answer is simple - solving chess diagrams with specific, recurring patterns over and over again until they become second nature. Tactical proficiency should be the first and most important goal of the developing junior and intermediate player.