The middlegame is full of tactics which aim to:
Most tactical ideas (such as forks, pins & skewers)
are achieved in one or two moves.
Some combinations are longer and can use a variety of tactics.
Video - Beginner to Chess Master
This video covers 9 tactics which commonly occur in games, including:
Video - Remove the defender (a good tactic for winning a piece)
Tactics training at Junior Chess - secrets of success