These reptilian humanoids, of which Bossk is the most famous, are skilled with a Concussion Rifle and are known to do the odd job for Darth Vader as a bounty hunter. They're also known to work for Hutts in the underworld - provided the price is right. Deadly at long range with the rifle, they move fairly slowly in order to keep their distance from you and maximize the rifle's effectiveness.
Suggested Method of Attack - Get in close. The trandoshan will cease fire in order to avoid hurting itself when you get too close and it has no other attack. Fists will finish it then, or a few quick blasts with any of several weapons. If you're unlucky enough to be in long range, stay behind cover to avoid the concussion blasts and fire quickly with your own Concussion Rifle while dodging blasts and trying to close the distance. Be sure to switch to a weapon that won't do damage to yourself when you get within a shorter range.