Excellent advice by Hunter there. Let me add a couple of more in-the-game musts when using the default team:
1) Pass a lot. Don't try long passes unless your player is REALLY free and unmarked, and the nearer defender is not that fast. Don't try runs or fancy stuff. Just pass and pass around, basically. Decent teamwork is very important.
2) Possession is everything. It will be very difficult for you to even reach 50% (I've seldom achieved that with the default formation) but you still have to try to give them the ball as little as possible, especially as the game closes to an end. If there are no open spaces ahead, in general a good advice is not to risk it --pass it back to a defender. Problem is that with the original formation, there usually aren't any open spaces, so quick passing is the way to go there. If an opposition defender is near a player of yours who is receiving the ball, first touch it to someone else. As crappy as their first touch is, their reaction is even worse, and if you try to control it, you'll usually just lose it.
3) If the opposition is attacking and they're anywhere between decent and great, don't play your way out of defense, ever. It'll usually end in a goal... for the opposition. Clear the ball with square, or, if you have a split second before an attacker closes you down, with circle. Then you can try regaining the ball before it reaches your box again.
4) If you're 1-0 up and the clock shows 60 min, it's time to switch to 5-4-1 (two DMCs preferrably). The same goes if you're 2-0 up at the break.
5) If you go 2-0 down at half time, switch to coach mode and invest your time in something else, 'cause 95% of the times the game is lost.
6) Don't charge at the attackers to regain the ball, they'll just run rings around you and your players will be knackered by the 75th minute. Rather, accompany them without sprinting, keeping in front of them, and when they close in on you or you see an opportunity, try to steal it.
7) As for signings, a good goalkeeper and two decent defenders will be of more use than some attackers. If you must buy an attacker, don't go for a heavy goal machine, as he won't even get to touch it. It's much more useful to get a player like Verón, who can create a play, make fast, accurate passes and take your FK and CK.
You may know all of this, but I think they are good tips anyway.
