I think an important goal should be to make early contact with other teams and put a lot of effort into diplomacy. Especially when it comes to wars, having allies will be vital. Even if an ally hasn't got the equipment to join an attack, it could create a diversion that would open the door for us. Equally important, we don't want to be backstabbed by a third party while we are on the offensive.
I have no experience with diplo in civ MP, but I played the game "diplomacy" for some time. It is of course a completely different game, but there some lessons one can learn from that game that will probably apply to our situation. Here are a few of those lessons:
- Be very communicative; strong bonds with other teams are won by communicating a lot. Making deals about all sorts of stuff, but also just exchanging little pieces of information. Keep the lines open and reply rapidly. When teams have to choose at some point where their loyalty lies, they often choose the team with which they communicate most.
- Don't be too angry; when someone attacks you, you should of course retaliate as best as you can. But don't start shouting at the other team or break off communications. Even during a war it is good to keep talking. You may at some point convince your enemy that its in their own interest to stop the attack. In other words: retaliate, but never whine.
- The ground situation always has the final word; no matter how beautiful the words of your partner are, always look at the sizes and locations of armies and the possible advantages that teams can have from an attack. Trusting your ally is easiest when he doesn't have the opportunity to backstab you.
- If you backstab, make sure it is final! Never betray an ally for a small advantage. A backstab should only be made if you can do it so thoroughly that it kicks your victim out of the race.