If you attack a piece and your opponent protects it, look out for the possibility of winning the piece by removing the guard. By capturing or driving away the protecting piece, you can render your target unguarded and ripe for capture. Likewise, if one of your pieces is doing an important job guarding another piece, make sure you don't let the opponent undermine it, or your whole defence could come crashing down.
This is the most straightforward way to remove the guard - by simply capturing it.
It isn't always necessary to capture the defending piece. Sometimes chasing it away is just as good. Forcing an enemy piece to leave its post is known as deflection.
Another means of removing the guard is by blocking the line along which it protects a piece or square. This is known as interference.
A related concept is the idea of an overworked piece. A piece is overworked if it is performing too many tasks at once and cannot carry them all out. Most often, this means a piece that is protecting two other pieces. If one is captured, and the defender recaptures, it relinquishes protection over the other piece. Here is an example of how to exploit an overworked piece.
An overworked piece may also be guarding against other threats, such as checkmate. A piece that is tied to defence like this is much like a piece that is pinned - it may appear to be defending other pieces, but those pieces can in fact be captured at no cost.
Here are some puzzles to test your knowledge of removing the guard and overworked pieces.