The way to beat knights is to deny them any advanced support points. -Steinitz
The job of a fianchettoed bishop (in front of your castled king) is usually not to get traded, but instead to guard the weak squares around your king, and stare menacingly down the long diagonal all game.
It's been said many times, in many different books and authors have said it a ton of different ways, but pawns are the soul of the game. They are the skeletal structure, they are the backbone of every really strong plan, and they are the backbone of how opening theory is created and then changed. It's all based on taking advantage of structrual weaknesses, things that basically come from the mindset that can't be undone, because pawns can't go back. And this is important because you want to develop plans that, basically the best move could be coming from your opponent, and it doesn't make a difference, because when you develop a plan that's taking advantage of a positional problem--something they can't undo--and you're able to execute that to perfection, you're able to beat very strong players, and that's how consistent chess is won. ...You want to develop plans that don't depend on your opponent missing anything. -Danny Rensch (Pawn Structure 101 video series)
Never lose control of any square on your side of the board. -Lifemaster A.J. Goldsby
Everybody who has played for a month or so learns ten or so tips on how to do an opening -- don't move a piece twice, both knights before the second bishop, etc. Then the next step is to learn when to consider exceptions due to a particular situation.
Then there are tips about the end game -- get the king to the middle of the board, block a passed pawn), etc. These have fewer exceptions, probably.
Tips for the middle game seemed to me to be rarer -- Here's a couple, the b2 pawn is often weak, but it might be poisoned. Pawn moves such as h3-h4 or h6-h5 are very risky next to a castled king.
Here is one from Roman Dzindzichasvili -- leave your pawns in place on the side away from where you are attacking, so you don't open lanes.
I saw this from Gserper on the KIA: "Generally it is a good idea to open up the center when you are facing a King's side attack." (But not so in the KIA, being his point).
That's what I am looking for. How about all the accumulated wisdom here help compile a list of things to consider doing and avoiding in the middle game that work more often than not.
Obviously there are many more middle game positions than beginning or end, so the tips will always be taken with a grain of salt, that's a given. But surely there are tips that work more often than not that people can share.
So what's your favorite mid-game tip?