When putting together a good group of defenders you should prioritise Players that have good Tackling and Strength, other attributes such as Fitness and Accuracy are not as important. Tackling oppossing players to try and get possession of the ball relies heavily on timing and selecting the correct type of tackle to avoid a foul.
There are two ways to tackle, the first is the standing tackle which is performed by pressing the B button (low kick when not in possession). This tackle will make your player put pressure on the ball and is the safest of the two ways to tackle and will only occassionally lead to fouls. The disadvantage of this tackle though is that if the player get passed you, you can no longer dispossess them using this method. The second way is the sliding tackle which is performed by pressing A (hard kick when not in possession) and must be perfectly timed otherwise it will lead to red cards and penalties. The advantage of the sliding tackle though is that it gives you the extra distance you need to intercept the ball.
The best strategy when you find yourself having to defend against the opposition is to use the B button more than the A button to try and get possesion back of the ball.