Ideas Behind the Chess Openings by Reuben Fine: General Principles

Theory of Openings:

1. In the initial position White, because of the 1st move has the advantage, consequently
2. White's problem in the opening is to secure the better position, while
3. Black's problem is to secure equality.

Two Fundamental Concepts in the Opening: Development & Center
Development is getting the pieces out.
The Center consists of the four squares in the geometrical center of board.
Basic principle in the opening is that it is essential in the opening to Develop all the pieces harmoniously and in such a way as to secure the most favorable position possible in the Center.

10 Practical Rules:
1. Open with the King's Pawn or the Queen's Pawn.
2. Whenever possible, make a good Developing move that threatens something.
3. Develop Knights before Bishops.
4. Pick the most suitable square for a piece and Develop there once and for all.
5. Make one or two pawn moves in the opening, not more.
6. Do not bring your Queen out early.
7. Castle as soon as possible, preferably on the King's side.
8. Play to get control of the Center.
9. Always try to maintain at least one Pawn in the Center.
10. Do not sacrifice without a clear and adequate reason.
a) Secure a tangible advantage in development.
b) Deflect the enemy Queen.
c) Prevent the enemy from castling, either permanently or for several moves.
d) Build up a strong attack.

Two questions before each opening move:
1. How does it affect the Center?
2. How does it fit in with the Development of my other Pieces and Pawns.

In almost all openings there is a 'Normal Sequence' of moves which will lead to a 'Normal Position'. An 'Ideal Position' is also reached by a 'Normal Sequence' of moves but represents the maximum positional superiority which one player can secure from a successful opening. Each player wants to obtain an 'Ideal Position' out of the opening while preventing the opponent from achieving their 'Ideal Position', or reach a 'Normal Position'.
If one knows the Opening Theory, they will know the main ideas, plans, advantages and disadvantages of the likely 'Normal' & 'Ideal Positions' achieved from the opening.

How to evaluate the position achieved from the opening? 5 Ways: Material, Pawn Structure, Mobility, King Safety & Combinations.

Strategy is the body of ideas and holds only as a framework.
Tactics are the individual variations, is what goes into the into the framework, which is why the result often varies so widely from the original conception.
Timing is another important concept, as in most openings there are several ideas for each side, not all of which may be realized in a single game.