I'm studying screenwriting in college, actually, so hopefully my advice is worth something. If you're intent on a script, then start with your characters. Every detail about them, become passionate about them. From there, put them into the situation and define a few key moments you want them to go through. Then, link up those moments. Take each plot point you set in already and connect them in a sensible, fun manner. The script will almost write itself from here. Just make sure that the characters are maintaining interesting, relatable conversation and as for humor, that's for you to define. Your humor is why people go to your channel!
Just my advice. Good luck!