- place a piece in such a way that it has many places to go to
"single line chess advice"

there are ALWAYS exceptions to rules
It depends on the position
True, but some general "single line chess advice" are true for 90% of the situations. Im looking for advice like that. And then its up to the player to find out when to use them.
- if a (valueable) piece is lined up with the king, look for ways to pin the piece down

Great idea in theory, but I suspect the list could end up very very long!! Indeed too long to be of any use. :0(

If you lose to a ten-year-old, then play a nine-year-old next time.
When you can't think of what to do next, DON'T push a pawn.

place Bill Hartston's book "How To Cheat At Chess" on the playing table to gain a psychological edge.

FIFTEEN RULES FOR THE ENDGAME
(many of which also apply to openings and middlegames)
1. Doubled, isolated and blockaded pawns are weak: Avoid them!
2. Passed pawns should be advanced as quickly as possible.
3. If you are one or two pawns ahead, exchange pieces but not pawns.
4. If you are one or two pawns behind exchange pawns but not pieces.
5. If you have an advantage do not leave all pawns on one side.
6. If you are one pawn ahead, in 99 cases out of 100 the game is drawn if there are pawns on only one side of the board.
7. The easiest endings to win are pure pawn endings.
8. The easiest endings to draw are those with Bishops of the opposite color.
9. The King is a strong piece: Use it!
10. Do not place your pawns on the same color as your Bishop.
11. Bishops are better than Knights in all except blocked pawn positions.
12. Two Bishops vs B+N constitute a tangible advantage
13. Passed pawns should be blockaded by the King; the only piece which is not harmed by watching a pawn is the Knight.
14. A rook on the seventh rank is sufficient compensation for a pawn.
15. Rooks belong behind passed pawns.
http://blog.chess.com/NimzoRoy/endgame-faqs
CHESS OPENING PRINCIPLES by SIX FAMOUS GRANDMASTERS
Dr. Emmanuel Lasker's rules for the opening (from Common Sense In Chess)
1. Do not move any pawns in the opening of a game but the King and Queen pawns.
2. Do not move any piece twice in the opening, but put it at once on the right square.
3. Bring out your knights before developing your bishops, especially the Queen's Bishop.
4. Do not pin the adverse King Knight (ie. by Bg5) before your opponent has castled
GM Reuben Fine on the opening:
1. In the initial position White, because of the extra move, has a slight advantage. Consequently:
2. White's problem in the opening is to secure the better position, while...
3. Black's problem is to secure equality.
Fine's rules for the opening
1. Open with either the e-pawn or the d-pawn.
2. Wherever possible, make a good developing move which threatens something or adds to the pressure on the center.
3. Develop knights before bishops.
4. Pick the most suitable square for a piece and develop it there once and for all.
5. Make one or two pawn moves in the opening, not more.
6. Do not bring your queen out too early.
7. Castle as soon as possible, preferably on the king's side.
8. Play to get control of the center.
9. Always try to maintain at least one pawn in the center.
10. Do not sacrifice without a clear and adequate reason, eg.:
* it secures a tangible advantage in development * it deflects the opponent's queen
* it prevents the opponent from castling * it enables a strong attack to be developed
Fine's two last questions to be asked before a move is made:
* How does it affect the center?
* How does it fit in with the development of my other pieces and pawns?
Nimzovitch's Seven Axioms (from My System)
* Development is to be understood as the strategic advance of the troops toward the frontier line (the line between the fourth and fifth ranks).
* A pawn move must not in itself be regarded as a developing move, but merely as an aid to development.
* To be ahead in development is the ideal to be aimed for.
* Exchange with resulting gain of tempo.
* Liquidation, with consequent development or disembarrassment.
* The pawn center must be mobile.
* There is no time for pawn hunting in the opening, except for center pawns.
GM Suetin's four principles for advanced players
* The fight for control of the center
* The striving for the quickest and most active development.
* The creation of conditions that permit early castling.
* The formation of an advantageous pawn structure
GM Hort's 13 rules for all players
* Take advantage of every tempo.
* Develop flexibly!
* Do not make pawn moves without careful planning.
* Begin the game with a center pawn, and develop the minor pieces so that they influence the center
* Develop harmoniously! Play with all your pieces
* Do not make aimless moves. Each move must be part of a definite plan.
* Do not be eager for material gain. The fight for time is much more important than the fight for material, especially in open positions.
* A weakening of your own pawns may be accepted only if it is compensated by a more active placement of your pieces.
* With the help of your pawns, try to get an advantage in space and weaken your opponent's pawn position.
* Do not obstruct your pawns by grouping your pieces directly in front of them; pawns and pieces must work together.
* During the first few moves, pay special attention to the vulnerable KB2 square on both sides.
* Remember that the poor placement of even a single piece may destroy the coordination of the other pieces.
* With White, exploit the advantage of having the first move and try to gain the initiative. With Black, try to organize counterplay.
GM Portisch on forming a repertoire:
"Your only task in the opening is to reach a playable middlegame."
SOURCE: http://exeterchessclub.org.uk/content/ten-rules-opening

Remember: "Pawns are the soul of chess."
A notion expanded by:
Kmoch - "Pawn Power in Chess"
Pachman - "Complete Chess Strategy"
Keres and Kotov - "The Art of the Middlegame"
Soltis - "Pawn Structure Chess"
Among others they provide a few more than single lines of advice. My logic is since the world in general turns out to be ass backwards (nothing is as it appears and is often the exact opposite), the lowly pawn must be the most important element to understand in chess.
However, if Watson is right ("Secrets of Modern Chess Strategy: Advances Since Nimzowitsch") you can toss many commonly believed single lines of advice.

Woah, great information. And awesome list NimzoRoy!
- a knight on the rim is dim
- It's harder for your opponent to handle multiple (potential) threats*.
* From youtube "bobby fisher trap". BF parks away a bisshop with an open diagonal. He doesnt do much with it, but its still a piece with dangerous potential. By setting up multiple pieces your opponent will have a harder time to see how the attack will be made.

Always assume that your opponent is better than you and will see the crappy 1-2 move traps you set up.

1.e4 and white wins!
But seriously,
1.Always assume your opponet will play correctly.
2.Having the bishop pair is worth a pawn (in the middlegame and endgame.)
3.When you are up material, trade pieces, not pawns.
4.When you are down material, trade pawns, not pieces.
5.Always have a plan.

Estragon forgot to credit that sage advice to Dr Tarrasch, who also has lots more pithy advice for all of us:
He who fears the isolated queen's pawn should give up chess.
Before the endgame the gods have placed the middlegame.
It is not enough to be a good player... you must also play well.
Mistrust is the most necessary characteristic of the chess player.
Weak points or holes in the opponent's position must be occupied by pieces, not pawns.
One doesn't have to play well, it's enough to play better than your opponent.
When you don't know what to play, wait for an idea to come into your opponent's mind. You may be sure that idea will be wrong.
What is the object of playing a gambit opening?... To acquire a reputation of being a dashing player at the cost of losing a game.
In a rook and pawn ending, the rook must be used aggressively. It must either attack enemy pawns, or give active support to the advance of one of its own pawns to the queening square.
As Rousseau could not compose without his cat beside him, so I cannot play chess without my king's bishop. In its absence the game to me is lifeless and void. The vitalizing factor is missing, and I can devise no plan of attack.
If the defender is forced to give up the center, then every possible attack follows almost of itself.
White has no positional equivalent for the centralized pawn.
All lines of play which lead to the imprisonment of the bishop are on principle to be condemned. (on the closed Ruy Lopez)
It cannot be too greatly emphasized that the most important role in pawn endings is played by the king.
The future belongs to he who has the bishops.
Chess is a terrible game. If you have no center, your opponent has a freer position. If you do have a center, then you really have something to worry about!
Every move creates a weakness.
For more quotes by the good Doctor click on this link:

I'm reading the Amateur's Mind by Silman. These are a few that really stuck out, even though I've been trying to follow these ideas for a while.
"The seemingly insignificant difference between Bishops and Knights is actually one of the most important imbalances on the chessboard"
"Amateurs often think that a good move must involve a direct threat. However, this is way off the mark'
"Don't ever play a quick, thoughtless move."
"...if you love to attack, you can't go after the enemy King in any and all situations"
"If the integrity of your position is based on a one-mover like ...Qxg2, then you are dead meat..."
"Material takes precedence over positional considerations for most players. This is a big flaw."
And a paraphrase from his book: When you play a game of reaction, your position deteriorates and it results in a painful death.
There was also something about tactics and positions coming from each other, but it seems like I didn't underline it. There is a lot of stuff I did underline, but I'm not going to type a whole book for you. :-p

Estragon forgot to credit that sage advice to Dr Tarrasch, who also has lots more pithy advice for all of us:
He who fears the isolated queen's pawn should give up chess.
Before the endgame the gods have placed the middlegame.
It is not enough to be a good player... you must also play well.
Mistrust is the most necessary characteristic of the chess player.
Weak points or holes in the opponent's position must be occupied by pieces, not pawns.
One doesn't have to play well, it's enough to play better than your opponent.
When you don't know what to play, wait for an idea to come into your opponent's mind. You may be sure that idea will be wrong.
What is the object of playing a gambit opening?... To acquire a reputation of being a dashing player at the cost of losing a game.
In a rook and pawn ending, the rook must be used aggressively. It must either attack enemy pawns, or give active support to the advance of one of its own pawns to the queening square.
As Rousseau could not compose without his cat beside him, so I cannot play chess without my king's bishop. In its absence the game to me is lifeless and void. The vitalizing factor is missing, and I can devise no plan of attack.
If the defender is forced to give up the center, then every possible attack follows almost of itself.
White has no positional equivalent for the centralized pawn.
All lines of play which lead to the imprisonment of the bishop are on principle to be condemned. (on the closed Ruy Lopez)
It cannot be too greatly emphasized that the most important role in pawn endings is played by the king.
The future belongs to he who has the bishops.
Chess is a terrible game. If you have no center, your opponent has a freer position. If you do have a center, then you really have something to worry about!
Every move creates a weakness.
For more quotes by the good Doctor click on this link:
Looks like Tarrasch loved bishops. I tend to prefer them to knights, even though I'm starting to prefer closed positions. Makes no sense, does it?
I know this topic is very vulnerable for trolls and funny stuff. Yet it would be nice if people would give good "single line chess advice".
What is such advice?
It's a piece of advice that can be written in one or two sentences and that could be usefull for a player.
Example:
- Don't trade off pieces when you're behind in material
I will edit in all (usefull) advice here: (edit: wont be editing in all advice just read it :) repeating would be useless.)
1) Try to position your pieces in the center of the board
2) Don't trade off pieces when you're behind in material
3) Place you rook on an open file
4) Force moves
5) Ruy Lopez: "Always position the board so that your opponent is looking into the sun."
6) if a (valueable) piece is lined up with the king, look for ways to pin the piece down
7) Before every move you check for: checks - captures - threats
8) Watch out for mates when your king is on the bankrank behind a row of pawns (or: move one of those pawns early to prevent such a mate)