Most soccer conditioning is based upon running...and rightfully so.
Typically a coach will have his or her players run distance or sprints. But never together.
This is a monumental mistake.
The game of soccer demands a player can "cruise" at lower speed and then turn on a 100% sprint at the drop of a dime. This is done throughout the entire game.
Therefore, interval training should be the basis of your conditioning work as that will have the greatest carryover to the soccer field.
Alternate periods of slower, duration running with sprints ranging from 85-100% of a players max.