While evaluating a position strategically, a player must take into account such factors as the relative value of the pieces on the board, pawn structure, king safety, position of pieces, and control of key squares and groups of squares (e.g. diagonals and open files).
Care must therefore be taken to avoid them unless they are compensated by another valuable asset, such as the possibility to develop an attack.
A fundamental strategic and tactical rule is to capture opponent pieces while preserving one's own.
This ignores complications such as the current position and freedom of the pieces involved, but it is a good starting point.
The king is priceless since its capture results in the defeat of that player and ends that game.
A player who has all pieces developed and no tactical tricks or promising long-term plan should try to find a move that enlarges their influence, particularly in the center.
In some openings, however, one player accepts less space for a time, to set up a counterattack in the middlegame.
In this diagram from the Nimzo-Indian Defense, Black attacks four squares on White's side of the board (d4, e4, f4, and g4).
Control of the center is generally considered important because tactical battles often take place around the central squares, from where pieces can access most of the board.
The initiative belongs to the player who can make threats that cannot be ignored, such as checking the opponent's king.
They thus put their opponent in the position of having to use their turns responding to threats rather than making their own, hindering the development of their pieces.
If a defender must be added at a later time, this may cost a tempo or even be impossible due to a fork or discovered attack.
The approach of always defending one's pieces has an antecedent in the theory of Aron Nimzowitsch who referred to it as "overprotection."
As a rule of thumb, exchanging pieces eases the task of the defender who typically has less room to operate in.
Exchanging pieces is usually desirable to a player with an existing advantage in material, since it brings the endgame closer and thereby leaves the opponent with less ability to recover ground.
[citation needed] When playing against stronger players, many beginners attempt to constantly exchange pieces "to simplify matters".
Conversely, "down the exchange" means having lost a rook but captured a bishop or knight—a materially disadvantageous trade.
A passed pawn on the sixth rank is roughly as strong as a knight or bishop and often decides the game.
As a result, lacking a bishop weakens one's ability to exert control over and parry threats from the deprived color complex, though there may be compensation in the form of tactical or positional assets, or from possible countermeasures, such as placing one's pawns on the color of the lost bishop.
A pair of rooks on the player's seventh rank are often a sign of a winning position.
With reduced material, a quick checkmate becomes less of a concern, and moving the king towards the center of the board gives it more opportunities to make threats and actively influence play.
Chess strategy consists of setting and achieving long-term goals during the game—for example, where to place different pieces—while tactics concentrate on immediate maneuver.
Because of different strategic and tactical patterns, a game of chess is usually divided into three distinct phases: the opening, usually the first 10 to 25 moves, when players develop their armies and set up the stage for the coming battle; the middlegame, the developed phase of the game; and the endgame, when most of the pieces are gone and kings start to take an active part in the struggle.
In some opening lines, the exact sequence considered best for both sides has been worked out to 30–35 moves or more.
An opening may end with castling, which moves the king to safety, creates a stronger back rank, and puts a rook on a center file.
Most players and theoreticians consider that White, by virtue of the first move, begins the game with a small advantage.
Black usually strives to neutralize White's advantage and achieve equality, or to develop dynamic counterplay in an unbalanced position.
The study of openings should therefore be connected with the preparation of plans typical for resulting middlegames.
Another important strategical question in the middlegame is whether and how to reduce material and transform into an endgame (i.e. simplify).
For example, minor material advantages can generally be transformed into victory only in an endgame, and therefore the stronger side must choose an appropriate way to achieve an ending.