I was visiting my LHBS recently and they mentioned that they were hosting a new home brew competition and might need some help. Since I'm rather new at brewing, I figured this would be a great opportunity to learn so I volunteered.
The competition was yesterday and, let me tell you, I learned more about beer and home brewing in one day than I had in months of reading forums.
As a steward in a BJCP style competition, your duties include things like keeping track of beer scoresheets, opening and fetching bottles for judges, basically giving them what they need to judge a competition. Usually there's plenty of beer left for you to try along with the judges. The judges that I had the pleasure to steward for were well versed and experienced home brewers. Getting their input on the beers we were trying was really invaluable.
During the second part of the competition, (there were two sessions, morning and afternoon) I had the opportunity to judge. I was paired with two very experienced BJCP certified judges. I learned quite a bit about my flight's style, including how to really taste, smell and observe the beer.
All in all, if there are any home brew competitions near you, I whole-heartedly recommend you at least steward for them.