Generally you will be wanting to do squats, lunges, calf raises to increase the power in your legs. generally heavy weights, doing 3 sets of 12 reps to increase strength.
General upper body circuits will keep you strong up top in order to hold off any other players attempting to take the ball from you.
Mainly though, you should focus on your agility and speed, being fast and agile is one of the key elements to the game these days and if you can out run your opponent, defender or attacker, you're sorted