General advice for middlegame This is a very basic and general question (and my first on this website), so feel free to tell me if this is inappropriate.

Besides specific strategies and opening sequences, there are some fairly general things about openings that are quite intuitive and, on the whole, not too difficult to follow: try to get out as many pieces as soon as possible and to position them on their most effective squares, try to get control of the center, try to castle when appropriate, put pressure on this square, do not move that pawn and so on. But when all the pieces are out, well placed, and I have castled, I have no idea about what I should do next. It might sound silly, but I feel that everything would compromise the balance I have just created. Are there any general pieces of advice, any general principles that one should try to apply? Or just any standard lines of thought that one could roughly follow? I feel like there is a huge gap between opening and endgame that I have no idea how to fill, and that I usually start out well in the opening and end being in disadvantage in the endgame because I did some silly moves in the middlegame because I did not know what to do.

For instance: I was playing a match against a computer opponent. I managed to get out all my pieces (horses on c3 and f3, pawns on d4 and e4, bishops on the sides, putting pressure on the f7 square and so on, all very classical) and to castle and the opponent had only been moving his horses around aimlessly by that time! He had not even moved a pawn! A good player would be sure to win, starting from such a situation. But in my case, whatever I tried turned out to be a bad idea and the counter actions of the opponent where always effective and in the end he won.

I should mention that I am reading "Logical chess move by move" by Irving Chernev. I haven't got vey far yet, but even the few pages I've read were very illuminating as far as positional play in the opening is concerned. But somehow I did not manage to take away any general advice on how to proceed in the middlegame: as I said, once everything is well placed, whatever I do seems to destroy its balance...
I feel you should choose an opening repertoire so you enter middlegames where you (a) know where the pieces belong ordinarily, and (b) understand the plans in those openings.  At a certain point, you need to do more than "just develop".

If you've ever watched a GM give a video lecture on some opening, you'll see them repeatedly avoid certain lines not because they're "bad", but because there is no clear plan for what to do.  And I can't tell you how many games I've lost simply because I got to a position with my pieces all on their seemingly best squares, but without a plan for how to continue.  I make random moves that don't immediately lose, but it makes things incrementally worse.

For example, a straightforward plan arising from an opening (that works from beginner to super GM level) is the minority attack.  Here's one of many examples:

[FEN ""]
[Date "1994"]
[Round "2"]
[White "Karpov (2780)"]
[Black "Campora (2560)"]
[Result "1-0"]

1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. cxd5 exd5 5. Bg5 Be7 6. e3 O-O 7. Bd3 Nbd7 8. Nf3 c6 9. Qc2 Re8 10. O-O Nf8 11. h3 Be6 12. Bxf6 Bxf6 13. b4 Rc8 14. Na4 Rc7 15. Rac1 Be7 16. Qb1 Bd6 17. b5 Qf6 18. bxc6 bxc6 19. Nh2 Qh4 20. Bf5 Qh5 21. Bxe6 Nxe6 22. Nf3 f5 23. Rc3 Nd8 24. Nc5 Bxc5 25. Rxc5 Ne6 26. Rc3 f4 27. e4 h6 28. Re1 Rce7 29. Rxc6 dxe4 30. Rxe4 Qd5 31. Rc3 Qf5 32. Qe1 Qd5 33. Kh1 Qd6 34. Qd2 Ng5 35. Rxe7 Qxe7 36. Qxf4 Qb4 37. Nxg5 hxg5 38. Qd2 g4 39. hxg4 1-0


In this game, white's plan after development is a minority attack: to push the queenside pawns, and give black a pawn weakness, which should give white an edge in the endgame.  We see on move 18, black ends up with a backwards pawn.  White heads for an endgame by swapping off pieces, while black tries to stir up trouble with the f-pawn push.  On move 28, black gave up defending it (rather than waste a rook defending a pawn), and let white capture it.

The moral of the story: choose openings so that your plan is clear.