Instructions
Keep him pinned down. The Rogue Jedi can easily be contained with Force Push and Blast Wave. Charging both will keep him down for a longer time, but leaves you open to attack. He likes to throw his lightsaber at you, so be careful.
Hit him when he's down. Hold the lightsaber attack button when the Rogue Jedi is on his back. Doing so will hit him for massive damage without him being able to hit back.
Cannonball him. Grip him and hit him with Force Push while you've got him gripped. This will send him flying and take a big chunk out of his health bar.
Jump to dodge his thrown lightsabers. He likes to do this attack more than just about anything else. It can be easily blocked or dodged by jumping over it. The trick is to give yourself enough room between Vader and the Rogue Jedi to avoid it. If you stay close and try to hit him all the time, it will be easy for him to blindside you with this attack.
Dodge his TIE Fighters. While the Rogue Jedi doesn't actually have TIE Fighters shoot you, he does call them down to the ground. If you're in the upper-right corner of the fighting field, you could get caught with one on top of you. This isn't fatal, but it hurts. Stick to the lower left corner and start running around when he projects a bubble and starts concentrating.
Finish him. As with all bosses, the Rogue Jedi allows you the chance to whip him with a cool set of finishing moves in order to wrap up the fight. Doing so will teach you how the finishing moves work for the other bosses. They are all different, but the technique is the same. Press the displayed button as quickly as you can and be ready to press more.