The tactics of diplomacy are simple. Once you know the political situation, you can determine the short term goals of your foes. Like if you are England, and France is already in the English Channel, with a second ship in the Irish Sea. If you try to move your fleets in London and Liverpool to Wales, there is a good chance that France will support one of them, and move into the center. But you can’t just let him convoy an army into Wales either. What do you do? One of Frances goals is to land an army in England, and going after Liverpool will not allow that. So he will attack Wales or London. Therefore you must support Liverpool into Wales. This will have the highest chance of success in the situation were Germany is at peace with France

What if Germany is starting to attack France? Then you have to try to get France to ally with you, but if that failed then you need to ally with Germany. For your moves though, you need to give your fleets hold orders. Then England can only take Wales. And you have nothing to fear, because he will not convoy an army into Wales, due to germany attacking him on land, and he will need that army for defense.

Be paranoid. Protect yourself from betrayal by your allies. If you trust your allies too much, you are just setting yourself up for betrayal. All that it takes is a few units hanging back to defend your centers. If you don’t allow your allies the opportunity to attack you, then there will be no reason for them to do so. The majority of stabs are because a player has all of their units on the offensive, so they can’t defend from an attack. if you get to be to powerful then allies may attack you as well. if you have units hanging back, then you will be in a better position to defend your centers.