Speed is a very important element of soccer. If a player doesn't have speed they can't beat defenders to a long pass to take the ball to goal or they can't keep themselves between the striker and the goal. A effective way to improve ones speed is to do a lot of running and ad additional difficulty when doing so, for example instead of just running sprints on a flat field doing them on up a hill can strengthen ones legs making them faster.
Agility can be the difference between beating a defender or being the one left in the dust. When two people are challenging each other more often than not the attempt is made with a very quick movement from one direction to the other. This requires great agility in order to make the movement in a coordinated motion while retaining possession of the ball. A drill that can be used to enhance this is by setting up cones 5-10 yards apart and moving left to right as rapidly as possible and moving forward or backwards at the same time.
An attribute that is necessary to perform many of the other elements is balance. When a player is shielding off the ball they need to keep themselves upright and in the right position to prevent the opposing team from gaining possession. Also when a player goes to strike the ball they need too keep their body placed right to get maximum power and the desired strike. A way to increase balance is to use a balance ball and stand on it for as long as possible.
In order to withstand the mental stress and concentration that one must endure and maintain it is important to be prepared. With the fast paced play of the game it is necessary to have ones head in the game to maximize their performance.