How to defend in FIFA 12?

After playing ~250 multiplayer matches now, I think I can add some of my own suggestions:

• Using contain/A outside of the one third is quite useless, because there is usually enough space for the attacker to make a safe pass and there usually won't be another defender close enough to help you.
• Instead, if you want to play apply pressure on your opponent early on, try to surprise him by running into him and tackling with B. This should be done with offensive players whom the attacker has already passed, so you don't leave any gaps open in your defensive rows.
• Anticipate passes. It's very hard in the beginning, but once you get to know the different types of players you will get a good idea to where they will likely pass. Even if you don't actually intercept the pass, running towards the pass target will give you a good chance to get the ball by pressing.
• In your defensive third, don't fall for dribbling. The worst thing you can do is pressing tackle or even slide tackle too early, leaving your player 'paralyzed' for a second and opening up the way to the goal. Be patient.
• In contrast to the above tip, don't be too patient. If you leave a good player too much time to figure out how to crack your defensive line, and especially if you let him run circles around your goal, he will sooner or later find a gap or a good position for a distance shot. If you notice he is up to something, break out of containing, try to get him with a tackle and call a second player to help you.
• Calling a second player is usually very helpful when you're trying to contain your opponent, but it will often leave you open for 1-2-passes or even worse, open a yawning gap in your defense line. Use it sparingly, and most importantly, if you notice that you are calling an essential defender, abort your call.
• Preventing the opponent from getting to your wings into a crossing position is hard to impossible. That's no big deal though. The important thing is that you do not let him cross. Always have a defender on his toes, right between the winger and the goal. This is the most important use of contain there is! Use sprint + contain to keep him from crossing, and watch out for possible breakthroughs into the penalty zone.
• Use LT + contain if you have an opponent who dribbles a lot, he will most likely bump into you.
• If your opponent managed to break away in midfield, don't call out your keeper too early or you will just get lobbed over. A good strategy is to fake running out with the keeper. Press Y and then release it again, before the opponent tries the lob.
• You can also tell your keeper to stay on the goal line by pressing Y twice. This sometimes helps with overenthusiastic goalkeepers.

These hints are meant for multiplayer matches, especially Head-To-Head-Season. I have no idea if they are any good against the AI.

This is quite a good article on Tactical Defending in FIFA 12:

FIFA 12 - Defending Guide

From my own experience I've found containing and then calling in a second player to be quite effective - when there are two defenders containing they seem to get closer than with just one and tackling is then much easier.

If you're running next to an attacker, the standing tackle button (B/circle) can be used to grab/bump/restrain the attacker, which I've found useful for winning the ball on a number of occasions.