Lessons from the book Questions of Modern Chess Theory

The fundamental unique law for playing any chess opening: 

* Develop your own pieces to good positions as fast and effectively as possible, while trying your hardest to stop your opponent from doing the same. 

* Fight for the centre. 

The Centre  

As we know, any piece placed in the centre (with the exception of the rook) is "hitting" more squares than it would elsewhere, which means that this is where it possesses its greatest fighting value. Furthermore it is from the centre that pieces can be transferred to either of the flanks in the smallest number of moves. These two circumstances make the centre the most important place on the whole chessboard.  
– Isaac Lipnitsky, Questions of Modern Chess Theory 

Some players may be forming the opinion that an early occupation of the centre with pawns is, in general terms, undesirable. Such a conclusion would be over-hasty and false, since there are many cases where pawns occupying the centre do bring an advantage. Everything depends on the concrete circumstances. I only wish to emphasize that a pawn centre should not automatically be thought to have decisive significance. 
– Isaac Lipnitsky, Questions of Modern Chess Theory  

…pawns, as being the most stable, are best suited to building a centre; nevertheless centrally posted pieces can perfectly well take their place. 
– Aron Nimzowitsch, My System 

It quite often happens that a player sets up his centre but then finds it to be nothing but a burden, as it serves as a convenient target for the opponent's counter-attack. 
– Isaac Lipnitsky, Questions of Modern Chess Theory 

Thus when the complex question arises as to whether you should occupy the whole centre with pawns or not, the right answer depends on what role your centre will play in the coming struggle. It is this that decides whether the strength of the centre will be real or illusory.  
– Isaac Lipnitsky, Questions of Modern Chess Theory 

… the centre is the soul of the opening. 
– Isaac Lipnitsky, Questions of Modern Chess Theory 

The Flanks 

Compared with the centre, the flanks in the opening play a lesser role. The centre occupies a dominating position with regard to the flanks. Therefore when the opponent undertakes an insufficiently prepared flank operation in the opening, we often manage to frustrate this diversion with a timely strike in the centre. 

The strategic rationale of such a strike is this. Gaining control of the centre allows us to create counter-threats that are more dangerous. Wishing to prevent this, our opponent will be forced to concentrate his main attention on the centre. And then the flank operations that he started earlier will be broken off. Exploiting the weaknesses that have formed there, we can often organize a strong attack on that same flank where our opponent attempted to do so. 
– Isaac Lipnitsky, Questions of Modern Chess Theory   

…premature flank attacks should be punished by play in the centre (= break through in, or occupation of the centre). 
– Aron Nimzowitsch, My System 

…the success of a flank attack depends to a decisive extent on the situation in the centre. 
– Isaac Lipnitsky, Questions of Modern Chess Theory  

The Initiative 

The route to victory lies through the initiative. 
– Isaac Lipnitsky, Questions of Modern Chess Theory  

The player who holds the initiative in the opening must constantly endeavour to increase and consolidate it, so as not to lose it; he must do this until he manages to gain an advantage of a stable kind – such as a material plus, the better endgame, an enduring attack against the king, etc.  
– Isaac Lipnitsky, Questions of Modern Chess Theory  

It frequently happens that the initiative can only be seized or maintained by drastic measures such as the sacrifice of a pawn or piece, or a complex combinative regrouping. If we do not resort to these measures in time, the initiative may not only slip away from us – it will very often cross over to our opponent, since the initiative in chess does not like to remain homeless.  
– Isaac Lipnitsky, Questions of Modern Chess Theory   

…positional sacrifices are well known to be the most difficult ones. In each particular case the decision basically depends not so much on calculation as on our experience, intuition and faith in our own powers. 
– Isaac Lipnitsky, Questions of Modern Chess Theory  

When you play a positional sacrifice 

You are not basing your play on calculations to regain the sacrificed material in the next few moves – indeed when your opponent offers you such an opportunity, if often pays to refuse it, in order not to forfeit your initiative. 
– Isaac Lipnitsky, Questions of Modern Chess Theory  

(There are sacrifices based on calculations, but they are not positional sacrifices.)  

It must not be thought that seizure or retention of the initiative in the opening must constantly involve sacrifices. We should resort to them only when they are indispensable. Time and again, powerful positional moves enable a player to gain or develop the initiative without sacrificing anything. 
– Isaac Lipnitsky, Questions of Modern Chess Theory 

The Opening 

The opening should be regarded as the phase of initial mobilization of the forces. When most of the pieces have been brought into action and the placing of the kings has been decided, we can regard the opening as completed. 
– Isaac Lipnitsky, Questions of Modern Chess Theory