After my first judging experience, here are my tips, by category:
Chicken - don't do pulled chicken! Make sure no pieces look burned. Don't oversauce.
Ribs - Show at least one rib with the side of the meat showing. Every judge at my table thought that was important. Keep cuts very clean. Double cut isn't necessarily a good thing.
Pork - If you do more than one style of pork (sliced, pulled, chopped), don't separate them too much; it makes the box look empty. Spray with sugar water/apple juice/whatever to keep it from looking dry if you don't sauce.
Brisket - trim off excess fat. Also, trim the brisket to the box... pieces that are too long detract.
On all, make sure that the box and the meat are tidy. If it's sliced, like brisket or chicken (if sliced), clean any rub off the cut part of the meat so it looks neat. Make sure things don't look dry!
CBJ, some comps, a few awards, Certified Artisan Steak Taster.
XL Big Green Egg, Bubba Keg Convection Grill, Weber Kettle, Charbroil Infrared and mad livefire cooking skillz! :)