Can't go wrong with pork butt. It is one of the most economical hunks of meat to practice with and pretty hard to totally mess up.
Keep it simple while you are learning, don't get to caught up with rubs, injections, etc... I would suggest running your cooker 250+, I personally like the 275-300 range. Cook it until it probes tender.
Meadow Creek TS250 With 42" Chicken Cooker
Cajun Fryer FF2