chuck roast.
One of the cheapest cuts of cow, and hard to screw up.
You'll love your WSMC, they're awesome!
Here is my suggestion for starting:
It's hard to keep a steady temp with your WSMC for the first go-round, so see if your local butcher can give or sell you some scraps of beef or pork fat from their waste trim. (you'll need at least 3 pounds, I did five)
They cannot legally sell it if it's in the bone barrel, but if you're lucky they'll be up to their armpits in rib roasts this time of year, and may have a pile of fat scrap on the bench, this stuff can be had for a song.
Fire up the smoker, spray the inside down with PAM, put the fat on it, and play with it. See how hot you can get it, see how cool you can get it. Play with each vent, observe and note what manipulating each one does so when it's show time, you know what you can do.
This will pre-season your smoker, and shake it down, so the soot and fat will dull some of the reflective properties of the inside of the smoker, and you'll know where you stand when the time comes to impress the family or friends with your cuisine.
From there, have fun with it.
There are lots of neat tricks to woning one. Some folks have been replacing the water pans with terracotta pans, which offer more of a consistent heatsink property. I fill my water pan with play sand and hot water.
What else?
Bend the ears that hold the water-pan in. They leave the factory without enough grip to hold a heavy water pan in place, but bending the ears in about 1/4" gives them a nice grip.
Another trick, and this one I learned from Smokin' Al, is to start your smoke cold, meaning, once your coals are going, assemble the unit, and put the meat on at once, that way the meat's internal temperature raises with the internal temp of the smoker, and helps the heat distribute across the meat evenly.
good luck!