Help your pieces so they can help you.
Source: Paul Morphy.
The situation you describe is quite common. You find yourself in a position where there is no clear course of action. In these cases, I urge you to:
- Identify your worst placed piece
- Implement a short plan to improve that piece (no longer than 3 moves)
In the example below, which is position 41 of the quizzes in Mastering Chess Strategy by Johan Hellsten, we see that it's an early middle game with no major attacking or defensive duties for either side. Neither are there simplifying opportunities.
With White to move, we note that the a1-Rook is not doing anything. How can we activate it? Well, Rooks belong on open or semi-open files. The f1-Rook is already on a semi-open file, so it would be great to play Rae1. But the Queen is in the way. This led to the following plan being executed:
[FEN "2bq1r1k/rp4pp/p1p3n1/5p2/3P4/1BP2N1P/PP4P1/R2Q1RK1 w - - 0 1"]
1. Qd2 b5
2. Rae1 Qd6
If you find that you really can't decide on a move, then
When in doubt, move a piece, not a pawn.
Source: The Wisest Things Ever Said About Chess by Andrew Soltis.
This is because if the piece move is poor, you can often rectify the mistake by moving it back. Not so with pawns.
In this example (game 149 of Mastering Chess Strategy), the centre is closed implying that play should be on the wings, so White plays 1. a4?!, instead of the flexible 1. O-O* (the King is almost certain to castle kingside anyway, and this also prevents Black's queenside play). The problem with 1. a4 is that Black gets a big space advantage and his King is still stuck in the middle, whereas 1. O-O doesn't suffer from this. Let's take a look:
[FEN "1rbq1rk1/1p1nbppp/p2p1n2/2pPp3/2P1P3/P1NB1N1P/1P3PP1/R1BQK2R w KQ - 0 1"]
1. a4 (1. O-O b5 2. cxb5 axb5 3. Nxb5 Nxe4 4. Na7) Nh5
2. Ne2 g6
3. g4 Ng7
4. Bh6 Nf6
5. Ng3 Kh8
6. Qc2 Bd7
7. a5 b5
8. axb6ep Qxb6
9. Ra2 a5
Last but not least, regarding planning. Yes, it is advisable to have a series of short term plans (usually 3 moves or so) and to remain alert to tactical opportunities and threats. From John Nunn's Understanding Chess Middlegames on the section called Losing the Thread (emphasis is mine):
Typical symptoms of this [playing poorly from a superior position] are planlessness, playing from move to move without any overall strategy, and spending too much time on moves.
*OK, castling isn't exactly a reversible decision, but it is more flexible, in the example position, than 1. a4?!