here are a few tips:
1. don't trim the pork shoulder--find a good bone-in piece of meat with lots of fat on it, leave the fat on, and place the meat on the grill rack fat side up. You can trim the fat off after it's done cooking if you want to.
2. don't let the smoker temp get above 250 deg. 275 is too hot. 200-250 is probably the best range. if you've got a decent smoker with enough air vent controls you ought to be able to keep the temperature pretty steady--225 degrees is kind of the 'magic' number.
3. baste the shoulder every hour or so. wrap it in foil the last couple hours of cooking (this will also keep it from drying out).
4. cook the shoulder to at least 195 deg.--I think kitchenelf said before that cooking it to 200 or so makes it even easier to pull.
5. Don't boil it!!!! sorry, i had to cringe when I saw that. it will probably end up more tender, but it will also suck all the flavor out of it. (Plus, it's "cheating")
hth--if i think of anymore tips I'll post them.