Every morning, get up an hour before you have to. As you take your morning shit, read a book by your favorite writer. I recommend Charles Bukowski.
Then sit down, every day, and just make your fingers move on the keyboard. Just write the first shit that comes into your head. Don’t worry about structure or getting jokes in there or expressing any particular idea. Write this material with the idea that NO ONE is EVER going to read it. You will have a voice in your head chiming in constantly saying OMIGOD THIS FUCKING SUCKS! YOU HAVE NO TALENT! IF ANYONE EVER SAW THIS IT’D BE LIKE EVERY GIRL IN JUNIOR HIGH SEEING YOUR NAKED DICK AFTER YOU WERE SWIMMING IN ICE WATER! You will need to get past this voice. It takes about a year.