I got lucky and started off judging. Frankly, I was surprised. I *thought* I could cook pretty darned well. Seeing what came across, both good and bad, taught quite a bit (picture worth a 1000 words; then see, smell, and taste it must be worth a gazillion).
Then, when I went to certification school, what I saw there were a lot of teams attending that had no intention of judging, just wanted to know what they were being judged on and apparently have had too many outings where they felt they did good and scored poorly. Frankly, if they'd have judged once or twice, I think they might've save the school effort. There should be a few local cookoffs in your area that'll groom an uncertified judge.
Then, by all means, jump in to a few small cookoffs to get your feet wet. You'll learn a ton from that as well. When you can, watch other competitors, and talk. Most are very helpful. What you'll find is that what works for one team doesn't necessarily work for another.
I will say, make the BBQ that you enjoy eating! Do not try to guess what judges want. HOWEVER, if you like BBQ that tastes either a) like a salt lick, or b) like you're
eating sugar out of the bag, or c) is so hot that it makes habanero pepper blush, you
might want to have a few friends honestly judge your Q and give feedback...
Oh, warning, judges should be stone-cold-sober when they judge. They have not
been drinking beer, yet. Q a little towards the salty side fares better when people have been drinking. Hint: when developing your competition rub(s) and sauce(s),
taste them stone cold sober; when drinking WATER.