My primary school's Christmas plays tended to be...slightly odd versions of fairytales. I say this as introduction to explain the fact that I played a tax collector and a moon robot in Jack and the Beanstalk, and Ratman (alongside my sidekick Bobbin) in the Pied Piper of Hamelin.
In secondary school I didn't really perform in any of the school shows because we only ever did musicals and I can't sing, so I did backstage stuff for those. The 6th Form always did a silly show at Christmas taking the piss out of the teachers, and I played the villian (the librarian) in that in Year 13.
In youth theatre I had a bunch of little bit parts, but the only time I had a major role was when the person who was actually cast in it threw a tantrum and refused to do it so I stepped in (it was a part for one person which had been split so that someone who could actually learn and deliver lines could share it with the kid with the speech impediment and learning disability, and she refused to work with him). That one was really fun though (despite the part where I wasn't allowed to hang upside-down off the scaffolding even though it was in the script
At uni I joined the Light Entertainment Society, which is the least serious drama society around and so actually gives me parts \o/ I've also helped out with some of the producing and directing because no-one else wanted to do it, and most of my involvement in drama has always been based on being willing to do stuff rather than on actually being any good
Last year one of my friends I met through that let me help him out with lighting and sound on another show he was working on, and that was really fun, so I'm hoping to do more of that in the future (it seems like a good balance between the part where I want to be involved and the part where I am rubbish at actually being on stage
I'm also in a band that does in-character shows, but there are nine of us and I'm the quietest, so I tend to end up getting skipped over when we're working out talking bits and mostly just stand in the background and play.