I assist writers who write jokes (and often write jokes of my own) for TV.
I get materials organized for our morning meeting, which includes choosing the topics we will talk about on that day's show. I gather all the jokes (and help write some), give them to Chelsea, she chooses ones she likes and adds some herself; I keep track and make the cue cards for the show. I get everything ready on set for the taping, we tape that night's show, and then I start to get everything together for the next day's meeting.
Here's the first step for high school students
Well, if you want to get into comedy, specifically stand-up, start as soon as possible. Go to an open mic. If you are looking for any job in comedy, having stand-up experience will only help you -- especially if you want to be a comedy writer, it will show people you know how to write jokes. Also if you are a frequent performer, it will show people you are a hard worker. Also, write. Always write. Write anything. Read anything. Writing & reading regularly will make you a better writer.
"You're wasting your time focusing on music / comedy / writing, you should be doing something practical." "That stuff will never matter; that stuff will never get you anywhere in life."