Some tips for being a good writer of funny things:
Don't ever wander. Use minimal setup for maximal punchline. Don't go off on too many tangents from your core concept, unless they are absolutely hilarious and you are 100% positive it's worth it. If there is an excess word or a joke that isn't exactly working, get rid of it.
Mess with the syntax
Use long sentences and short sentences alternately. Flip phrases around, sometimes a simple strange phrasing can make a filler sentence strangely satisfying. Don't be afraid to venture outside of the typical creative boundaries. But most of all:
Proofread. The most important part about writing a joke is that people will be able to read it without stumbling. Flow is everything; writing should come first, jokes should come second.