If you have Saber Defense to the top in Force powers, it is easier to kill enemies with lightsabers. Defend their blows and sometimes they will get hit and get killed.

When you get to the harder levels, you will find out that Dessan (Dark Jedi) had followed you to the Valley of the Jedi and was giving his fighters the power of the Force and created fake Jedi. You will have to fight these people throughout the game. If you do not want to waste your time fighting them, then use Force Speed. You will move incredibly faster than your opponent and can attack them while his lightsaber is going too slow.

After you get Force Grip, use it and Saber Throw to kill the "fake" Jedis. This take longer as you progress in the game, but it still works. To kill opponents faster, change your lightsaber mode to red (strong).