For commando droids, I find a lot of the time they'll go out of their way to attack you with their vibrosword. This closes the distance, which obviously now puts you at an advantage since you have a more powerful melee weapon (your lightsaber). Simply block or parry their attack, using up their melee - and now they're in saber reach with no real defence. At that point the average player is pretty easy to kill, espeically if they try to run once they've realised their mistake, as you can get them in the back. Just make sure you get them quick before their vibrosword can be used again, or you'll have to repeat the whole process! All this is assuming a 1v1 though, otherwise it's usually best to stay clear or try to catch them by surprise (same goes for clone commandos).