A few tactics

Attacking and defending pieces

A piece is said to attack an opponent's piece if, in the next move, it could capture that piece. A piece is said to defend or to protect a piece of the defender's color if, in case the defended piece were taken by the opponent, the defender could recapture right away. Attacking a piece forces the opponent to respond only if the attacked piece is undefended, or if the attacking piece is of lower value than the attacked one.

To save an attacked piece one has three options: to capture the attacking piece, move the attacked piece, or move another piece in between the two.

Forks

A fork is a move that uses one piece to attack two of the opponent's pieces at the same time, hoping to achieve material advantage (because the opponent can only counter one of the two threats). Knights are often used for forks: they jump to a position from where they attack two pieces. A quite common situation is a white knight jumping to c7, thereby threatening both the rook at a8 and the king at e8. Such "king forks" are particularly effective, because the opponent is forced by the rules of the game to counter the threat to the king; the opponent cannot choose to defend the other piece, and thus cannot use a zwischenzug (see below) to complicate the situation. Queens are extremely useful as forking pieces, because they can move in eight different directions; in theory, a queen could attack up to eight different pieces at once. Pawns can also fork enemy pieces: by moving a pawn forward, it may attack two pieces: one diagonally to the left and one diagonally to the right. A common situation is the move Pawn d2-d4 forking a black bishop at c5 and a black knight at e5.

A queen move also often attacks two pieces at the same time, but this is only useful if both pieces are undefended, or if one is undefended and the other is the opposing king. The queen is more valuable than the pieces it is attacking, so it is usually not profitable for it to capture a defended piece.

Pins

"The defensive power of a pinned piece is only imaginary." - Aron Nimzowitsch

A pin is a move which forces one of the opponent's pieces to stay put because moving it would expose a more valuable piece behind it. As they move in a straight line, bishops, rooks, and queens can pin other pieces.

In the left diagram, black can't move the knight without losing the queen, and Black's rook can't be moved at all. In the right diagram, Kramnik pins black's bishop and soon wins it with a4-a5.

2-Way Protection

Placing two rooks in a straight line, as shown in the illustration above on the right, will cause both pieces to be protected from attack. Knights can also be used to protect each other. (Bishops cannot, because each bishop is on a different color of square. Pawns cannot do this either, because a pawn can only capture pieces ahead, and not behind.)

Skewers

A skewer is a move which attacks two pieces in a line, similar to a pin, except that the enemy piece of greater value is in front of the enemy piece of lesser value. After the more valuable piece moves away, the lesser piece can be captured. Queens, rooks, and bishops can skewer.

Because of possible pins and skewers, one should be extremely cautious if king and queen are located on the same vertical, horizontal or diagonal line, or can be forced into such an arrangement. This is the best technique to capture the rook or the queen.

Discovered attacks

A discovered attack is a move which unmasks an attack by another piece. A piece is moved away so as to unmask the attack of a friendly bishop, rook or queen on an enemy piece. If the attacked piece is the king, we speak of a discovered check. Discovered attacks are powerful, because if the moving piece manages to pose a second threat, the opponent is in trouble.

A special case of a discovered check is a double check, where both the piece being unmasked and the piece being moved attack the enemy king. A double check requires that the opponent moves his/her king as the king is under attack from two directions and it is impossible to counter both at the same time in any other way.

Pawns

Pawns are extremely useful in the game and are far more powerful than what meets the eye. When a piece cannot be captured without the attacking piece also being captured, pawns will suffice for that purpose. A single pawn approaching will force a more powerful piece, such as a rook or a knight, to retreat. A simple move of a pawn may reveal a hidden threat (see above) . Also, when pawns are arranged in a diagonal line, with the frontmost pawns guarded by the pawns behind, it forms an almost impenetrable wall capable of protecting any piece directly behind it. Furthermore, a pawn which has progressed all the way to the opposite side of the board may be exchanged for any "power piece," usually a queen.

To prevent this, one should have at least one rook (or queen) at your end of the board to capture any new queens as soon as the opponent gets them. One should also try to block the pawn, or urgently attempt to capture the opponent's pawns as they approach the end of the board.

If you are trying to get a new queen, try to capture any piece obstructing the path of the pawn. Put a rook at the opponent's end of the board, if possible. This will stop your opponent from trying to put a rook there. Then, place a rook behind the pawn you wish to turn into a queen, to recapture any piece that may capture the pawn.

Zwischenzug

The German zwischenzug means "intermediate move"; it is a common tactic that occurs in almost every game: instead of countering a direct threat, which the opponent expects, a move is played which poses an even more devastating threat, often an attack against the queen or the king. The opponent has to counter that threat first, and this will ideally change the situation to a disadvantage.

When a player plans the tactics, he or she should always watch out for a zwischenzug. Don't assume that the opponent has to counter all threats immediately. It is good practice to always check whether the opponent has a check or a move threatening the player's queen. Conversely, it is good to anticipate the opponent's threats and plan a surprising zwischenzug.

Sacrifices

Often it is necessary to throw the opponent's position or tempo out of balance by first sacrificing some material, sometimes to be regained with interest a couple of moves later. Pawn sacrifices in the opening are known as gambits; they are usually not intended for material short-term gain but instead to achieve a more active position.

Direct attacks against the enemy king are often started by sacrifices; a common example is a bishop sacrificing itself on h7, checking the king on g8 who has to take the bishop, after which the white queen and knight develop a fulminant attack.

Zugzwang

In chess, zugzwang (German for "compulsion to move") occurs when one player, because it is his turn to move, must make a move but every possible move weakens his position. The player is put at a disadvantage because he would like to pass and make no move, but a move has to be made. Situations involving zugzwang occur uncommonly; when they do occur, it is most commonly in the endgame, where there are fewer choices of available moves.

Attacks against the king

Attacks against the castled king are usually justified by some imbalance: the attacker has more firepower on the king's side than the opponent, or the opponent weakened his king's position by moving one of the pawns in front of the king.

Many mating attacks are introduced by sacrifices: if mate is close, then material advantage is irrelevant. The queen is usually the most important piece in a mating attack, because the queen has various ways of mating a king. The most common is a direct "contact check" while being protected by one of her own pieces. For example, white knight g5, black king on g8 and the queen mates at h7, or white bishop at f6 or h6 and the white queen on g7 mates the black king on g8.

Not every move in a mating attack has to be a check. Often, a check only drives the king to a better position, or weakens the attacker's setup. "Quiet" moves often complete the action.

Queens

As the queen is the second most important chess piece, capturing the opponents queen is a worthwhile task. Capturing a queen must either be done by stealth, brute force (such as attacking the king and queen at the same time) or both. A knight is often the best means of capturing a queen. If one uses a bishop or rook, it puts the bishop or rook in danger of capture. However, a knight that is attacking a queen is often unseen by the opponent and is immune to capture by the queen, because the queen cannot jump over pieces or move in an L-shaped motion.

An alternative means is that of using a protected piece to pin the queen in front of the king. With this method, it is impossible for the queen to escape.