If you've already started writing, that's great! Keep that up. Eventually, you'll end up with a repertoire of jokes, and when it comes time to perform, you can pick the best ones to go on-stage with.

It's not enough to just write jokes; you must deliver them. Choosing what words to say is one thing, but choosing how they're said is just as important. So practise saying your jokes out loud. Emphasise different words, change words around, change the speed of your speech, and see what deliveries you think work best.

Know your audience. You'll know better than we how strict your school is, but you'll obviously have to avoid discussing certain topics and using certain language. That said, you're performing for students, parents, and teachers, so you'll have to make sure your jokes can be understood by all three of those groups.

Be confident. This is super-important. When you're about to go up there, you will be nervous; I can assure you of this. The goal is to not be nervous once you get up there and start talking. As for how to be confident, it's difficult to explain cos it's something most of us learn through experience through repeated stand-up performances, or through doing Drama classes or school plays (and even if you have done those things, telling your own jokes for the first time, on-stage alone, can still be daunting). Even if a joke bombs, don't worry; it's better to keep going than to call attention to it.

Start with your second-best joke, and end on your best joke. Starting with your second-best joke is a good way to give yourself confidence as it'll demonstrate that, yes, you are funny, and you'll take it in your stride. And it's always good to leave on a high note. If you can't really determine which jokes are 'best' or 'second-best', start and end with jokes the ones that you're the most sure of, the ones you think have the highest chance of getting a laugh.