I actually don't. I have found that just making my voice gravelly seems to work. I don't try the Kiwi accent because I am an old school, Jason Wingreen kind of guy.
Honestly, the way that I learned to "be Fett" is from watching Fett at Disneyland. You have to be able to improvise, but having some canned phrases go a long way to that. I lifted, "You look like my kind of scum" directly from him. Even though it is a Jabba quote... it works.
Also, economy is key. You don't want to talk too much. Most of the quotes above are both conversation starters and enders... which is why being prepared with the right phrases is key. I am interested to see what everyone else does. I have only been at it a couple of years.