Is there some sort of opera etiquette? I always imagine people dressing all fancy shmancy with their little binocular things and yelling "Bravo!", but I don't know... It seems so antiquated to me (and not me at all, ahem).
Also, what section(s) are decent? I know the wheelchair section is like 20 bucks but that isn't my thing and I don't want to get crappy seats. Are balcony seats good?
I have been to the opera a number of times and never seen any binoculars, or heard people shouting 'bravo' for that matter (actually I might have once...). People clap after songs and, sometimes, a particularly impressive vocal feat (if there is time to do so)... don't clap when someone is singing. ;) Oh, and read the synopsis if you want to have any idea of what is going on - the story lines can be very hard to follow if you don't know what is going on. During the opera the music is more important than the story line (it takes a long time to cover a small amount of plot). Enjoy the music, not just the singing but the orchestra as well.
People also don't dress that poshly anymore... but wearing jeans and trainers would probably not be the best look. I tend to wear smart trousers, a nice pair of shoes and a blouse (or something along those lines).
Opera isn't that different from seeing a play at the theatre as far as etiquette goes.
Have fun!