Mastering the Chess Openings
Gambit Publications Ltd 2006
The center is a primary concern in deciding how to proceed with your plans, not to mention your next move.
This refers to moving pieces (not including pawns) off their initial squares and putting them "in play". Just counting counting the number of pieces that you have moved is the simplest measure of development. Of course, it's essential to consider the "quality" of development, that is, how well the pieces are placed.
One of the most important guidelines in chess is to protect your king from harm. This elementary consideration is sometimes forgotten. It can strongly affect the proper conduct of the opening stage.
Space & Its Properties
When you control more territory, you can often move your pieces from one theater of action to another more quickly than your opponent can, and thus attack on that front before he can defend.
Bishops like open diagonals and should usually be developed accordingly.
Knights also need as much freedom of movement as possible, but only to the extent that they don't unduly interfere with the activity of other pieces.
Rooks like to have open files, preferably ones that extend vertically as far as possible into the enemy camp.
The queen tends to stay at home or to lurk behind her pawns and pieces in the early stages of the opening.
Activity and Initiative
Active pieces control more squares. Such pieces aren't necessarily involved in a direct attack but can serve to harass opposing forces, support a pawn advance, and generally accrue more territory.