Most everybody knows the opening guidelines: control the center. develop your pieces, etc., but lesser understood seems to be a basic understanding of what to do with things like a lead in development, center control, a space advantage and the initiative. Many of my opponents think that after 1...a5 they have a license to violate sound opening principles and attack like a wild man, often playing unsound sacrifices, just because 1...a5 is a very poor first move.
When I first started studying middlegame books most all of them pounded it into our heads that you had to control the center by occupying it and cramped positions lead to defeat. And, if you controlled the center you had to guard against its destruction and it conferred upon you the right to attack. If your opponent controlled it, you had to counterattack in the center with everything you had. And they always discussed the value of a tempo...lose a move and your opponent had an advantage. Lose two and you were on the verge of defeat. Lose three and you might as well resign. The opening was all about Space and Time!
Then they talked about static (permanent) advantages and disadvantages: usually space, material, P-structures, etc. The other thing was dynamic (temporary) advantages and disadvantages: lead in development, the initiative, etc. Sometimes you'd read about one side having the initiative, but it was never explained exactly what the initiative was. That was what the Soviet School specialized in back in the 1950s...Soviet masters were often willing to trade a positional weakness (static disadvantage) for a temporary (dynamic) advantage...like the initiative. It was all very confusing.
In his book, Technique in Chess, Gerald Abrahams noted that giving rules only classifies ideas, they do not allow the student to create them. Speaking of the initiative, he noted that what is important is that the attacker have a 'feeling' that he has some advantage of tempo, some greater degree of mobility than his opponent. When it comes to generalities about time and space there are no rules to guide one to successful attack or defense. These are matters of awareness, vision and imagination, not technique. He also observed that awareness cannot be taught, adding that experience makes us more sensitive to the possibilities in a position. Abrahams gives an example of the maxim that one should not move a piece twice in the opening and at the same time reminds readers that that is not dogma. Development is a relative term.
What Abrahams was talking about was pattern recognition and that can be learned. “The chief factor in chess skill is the storing of patterns in the mind, and the recognition of such patterns in actual play.”- C.J.S. Purdy.
Dan Heisman article on pattern recognition
Improve Your Middle Game-Pattern recognition is one of the skills that makes a master. It's not inherent; it's learned. Mark Weeks
ChessOKdotnet offers a book for download titled Improve Your Chess Pattern Recognition. They also offer downloads for other books and chess programs, but I cannot vouch for their legality...download at your own risk!!
WGM Natalia Pogonina gives a good lesson on the initiative in this Chessdotcom post.
In the following short Game 15 played online, my 1600ish rated opponent went from a good position to a really bad one in a hurry when he allowed me to seize the initiative. He blundered his Q right at the end, but he was lost anyway.
I used to blunder pieces a lot. It was very frustrating to have a decent game only to throw away the game by dropping a piece. I solved the problem by doing a 'board scan' after my opponent moved and before I moved. It involved visually scanning ranks, files and diagonals. Not only did the piece-dropping stop, but I started noticing things, important things.