I use different formations all the time, but usually a back 3 or 4.
With a back 3, Use a sweeper in the centre, put the individual defence status of each defender to high, and put back line strategy to C along with offside trap. This will make them sit back, just keep getting in the way of anyone near the goal. This frustrates the hell out of my mates, cos they may get a break, and the box is covered, and I just defend well. Very rarely concede against player or cpu with this method. Also it would be safe to including a defensive midfielder watching gaps and helping out.
With a back 4, Make sure you haven't got them pushing out too far, but make sure they also don't sit too deep. The offside trap is more effective with a back 4, and you can risk pushing up a little further, getting your full backs in on attacks. Just make sure you have a good defensive midfielder, always staying back to cover any gaps left by forward running players. Also put the indvidual defence to high on CBTs, and normal on SB's. Then High for DMF. With a back 4 it is best to zone press and counter attack.
Stop your keeper running out by putting his individual defence to high. Then he will only come out when you press triangle.
The ultimate in defending is the cooperative mode, as long as you have an equal team mate. Me and one friend in particular have got a natural rythm going in co-op. We don't speak and know what's going on all the time, we have never been beaten when we've been on the same side and we've played a lot of wannabes. Saying that we've been gaming together for 15 years, so you'd kind of expect it.