Isn't this more of a strategy question?
Daddy, here are a few things I've picked up regarding team play:
1. Communication. The team that communicates well is successful. Whether you use in-game chat, live chat, PMs, IMs, Skype, or what have you, every team member needs to know the game plan.
2. Chemistry. Sometimes players just click. Other times, good players don't match up well together. Find players you're comfortable playing with, that you work well with.
3. Attacking and Forting. Generally, you want to attack the opponent who goes immediately after you and fort to the teammate who goes immediately after you. For instance, in doubles, Red should attack Blue and fort to Green. In Triples, Red should attack Yellow and fort to Green.
4. Bonuses. I play mostly No Spoils games, and preventing the other players from taking bonuses is important. Concurrently, if you can get your teammates bonuses, you'll win. The team with the higher salary generally wins (and this is true for Flat Rate and Escalating as well, although when cards are involved, bonuses are not quite as key. They're still important, though). As a corollary to this, the best bonuses to take are the ones that involve killing your opponents' men. For instance, it's generally not worth it to take two teammates' terts in order to hold a 4-tert bonus unless your teammates are reasonably safe from elimination elsewhere.
Break your opponents' bonuses, keep each opponent below 12 territories, get bonuses for you and/or your teammates, and take out weak opponents. In Quads and Trips, identifying potential targets for elimination early on is a fundamental move.
1 and 2 are essential. 3 and 4 change depending on the map - sometimes you need to attack another opponent rather than the one who plays immediately after you, for instance, or you have to decide whether you'll take your own bonus or break the other team's. No plan survives first contact with the enemy.
SoC team training is very helpful. If you haven't signed up yet, there's a waiting list in the SoC Training Fields forum. I'll send you an invite for a doubs game, too.