I have a used smoker (an older model called the SM008, which is now the SM009) you want something with a lot of fat in/on it to help with the initial cure of the walls of your smoker. So either a pork butt (for pulled pork or carnitas) or a Walmart brisket. Now I say WalMart brisket because those are pretty fatty. BUT there is a video you should watch first put out by Cookshack on YouTube about "curing" your smoker empty. Here it is, this works for any model Cookshack smoker:
http://www.youtube.com/watch?v=b54NrXU9OxQThen after you have done your setup/cure run then smoke your product. Man I am telling you this is so much fun !! I got a batch of baby back pork ribs I just slid in (rub, brown sugar and cherry wood for the smoke).
Enjoy and like Smokin' says take good notes.