Tackling in soccer is quite different from tackling American football style. In soccer, the tackle should be executed solely to play the ball, not the player.
Remember, you make a tackle only when you are confident you can disrupt the play and win possession of the ball, or when it becomes an emergency. A clever forward loves an opponent who constantly "dives" into the tackle; a quick sidestep by the forward and the defender is beaten.
The alternatives to tackling are important tactics of the game. They include:
Jockeying -- When the opponent has the ball and the attacker momentarily loses control of it, an alert defender can tackle away the ball.
Closing him down (pressurizing) -- This will limit his options and make him commit himself before he may be ready to.
Certainly defensive players make the most tackles, a skill they should develop, but midfield and forward players can retrieve a "lost" ball by a well-timed tackle. Diagram 1. The Block Tackle
Two players meet the ball at the same time. Impact is made with the greater area of the inside of the foot. Player 1 probably will win posession because she is lower and over the ball, and because she makes a quick second effort to force the ball over her opponent's foot. Diagram 2. Sliding Tackle
Player 1 slides into the tackle to disposess his opponent. This can be executed from the side or from behind the opponent. His technique involves correct timing, left hand/arm and leg cushioning his slide while the right leg is extended firmly while kicking the ball away. Eyes must be on the ball.
A good tackler needs to be tenacious, strong and determined, but not necessarily big. A good defender will mostly stay on his feet. Certainly I do not encourage sliding tackles be attempted on a synthetic surface or on a surface without grass, because of the risk of severe abrasions.
(*Jockeying means retreating, staying close and goalside of your opponent, delaying his progress while allowing your teammates to regroup.)