After the opening comes the middle game, somewhere around move twenty usually. This is where you and your opponent set off to do battle in the game of chess. A trade off of pieces, sacrifices, pins, skewers, etc characterizes the middle game. The goal of the middle game is to capture more of your opponent's pieces that your opponent can capture of yours. The methods that you use to capture your opponents pieces are referred to as tactics. Tactics are immediate plans, usually completed in a few moves, while strategy refers to longer-term plans in the game of chess.
Utilizing tactics in the middle game boils down to trying to capture your opponent's pieces for free or by sacrificing low valued pieces. Capturing opponent's pieces for free means that you can capture them without losing the piece that you used to take it. Sacrificing for a lower valued piece could be characterized by capturing a bishop or knight with a pawn. Being able to capture your opponent's pieces for free or by a low valued piece sacrifice gives you a great advantage in the game.
When playing more experienced opponent's it will be much more difficult to find free pieces or to sacrifice lower valued ones for higher valued pieces, however everyone is liable to make a mistake during a complicated game of chess. Awareness of the entire board and the openings available for you to attack is a must in the game of chess. Capturing more of your opponent's material than they can capture of yours will help you to ultimately win the game and to do so with ease. Always be on the look out for your opponent's unguarded pieces.