Sketch comedy is different from stand-up. It's not about punchlines; it's about The Game.
What is The Game?
The Game is the single unusual thing that drives the scene. It is the "What If?" * SNL Cowbell Sketch: * Normal Reality: A band recording a song. * The Game: One guy is obsessed with playing the cowbell way too loud. * Escalation: Every beat of the sketch raises the stakes of that specific unusual behavior.
Structure: Heightening
A good sketch follows a curve of Heightening. 1. Establish Normality: Two guys eating lunch. 2. The First Beat: One guys eats a whole raw potato. (Weird). 3. The Second Beat: He eats a raw onion. (Weirder). 4. The Third Beat: He eats the plate. (Insane). 5. Out: The scene ends before it gets boring.
One Idea Only
Don't try to stuff five funny ideas into one sketch. Pick one funny idea and explore it to its absolute limit. If you have a second funny idea, write a second sketch.