Basic tactics
A tactic is a short, forcing combination that wins material or delivers mate. Almost every game below intermediate level is decided by a tactic one player saw and the other didn't. Here are the four basics.
Fork: one piece attacks two targets at once (the knight is the king of forks). Double attack: the same with a long-range piece, like the queen. Pin: you freeze a piece because behind it is the king or something more valuable. Skewer: you give check and, as the king flees, the piece behind it falls.
The common pattern: two targets on the same line, or within a knight's leap. When you spot it, it's material in the bag.