Best Piece of Diplomacy Advice

[Octavious]

Don't enter orders when drunk

Don't take the game too seriously

If you're not having fun, you're doing it wrong

[VillageIdiot]

If There's Two Ways To Skin The Cat, Pick The Fancy One 
the fancy one is less expected

A deal is a deal. No more, no less.
take deals serious, but a deal is not a contract and if it no longer makes sense break it

Have at least one friend and one enemy.
friends are important, players without enemies make neighbours nervous

[Balki Bartokomous]

If There's Two Ways To Skin The Cat, Pick The Fancy One 
the fancy one is less expected

What is the fancy way to skin a cat? Also, why are you trying to fake someone out about how you are going to skin a cat?

[VillageIdiot]

If There's Two Ways To Skin The Cat, Pick The Fancy One 
the fancy one is less expected

What is the fancy way to skin a cat? Also, why are you trying to fake someone out about how you are going to skin a cat?

Using a magnetic hypersonic resonance decapacitor, deplete invisible bond holding together cat's skin molecules.

[VillageIdiot]

The non-fancy way is to tie one end of string to doorknob and the other end to the cat's skin and slam the door.

[Octavious]

I despair of some of the notions our overseas cousins have picked up over the years...

The fancy way to skin a cat is exactly the same as the non fancy way, except one does so whilst wearing a smoking jacket and holding a glass of claret.

[Doug7878]

Advice given to me by Hellenic Riot in one of my first few games on webDip:

1. Play against your opponent's two best move sets (ignore the many inferior moves he could make).
2. When evaluating your opponent's options, take into consideration the ending position each will leave him in.

[Doug7878]

... I should say AFTER one of my early games ...

[hthefourth]

A thought from John Cleese: delay making creative decisions.

In Diplomacy terms: formulate multiple strategies and ruminate on them until the moment when you have to choose between them. If you're clever you can do this without having your press sound wishy-washy.

[KalelChase]

Similar to the dots and lines above, one advice that changed how I look at the game is...

"Diplomacy is the art of getting the other players to move their pieces away from you."

[Beneficial Insurance]

Similar to all the above, but I recieved this gem from knilgau recently. It was in the form of a paragraph but it boiled down to this:

Use your words first.

Try and be diplomatic before you try and send you armies/navies to steal someones stuff.