I was super touched that @nathanrossi asked for this. Especially when I'll never be as good a joke writer as @bjnovak, an honest-to-God master. Regardless, here's what I have to offer.
  1. DO: Standup. Get a visceral feel for what actually makes people laugh out loud, and what doesn't. Experience the stomach-churning sensation of bombing. And the reward-center-of-the-brain eruption of hearing real laughs. You'll instinctively start gearing your writing toward "what works."
    Twitter and Facebook are awesome, AWESOME outlets for joke writing, but will never compare to the live thing. And I'm not just saying that because I'm an old man who is desperately out of touch.
  2. DO: Study the masters. Rodney Dangerfield, Joan Rivers, Redd Foxx, Don Rickles, Paul Lynde, Steven Wright, Jerry Seinfeld, Mitch Hedberg, Dave Attell, Sarah Silverman, etc.
    Get way overly analytical about their jokes, like it's a formula that you're desperate to crack. Have an equally obsessive comedy friend who you stay up late with, dissecting comedy and laughing a lot.
  3. DO: Write jokes because you think they're funny - period. If you try to write jokes that you don't actually laugh at yourself - but figure, "That's the kind of stuff they want on this project" - they'll always smell it. ALWAYS.
  4. DON'T: Let your inner censor get in the way. About 50% of the most successful jokes I've pitched were things I was afraid to say out loud. "No, that's just too stupid/ smart/ obscure/ hacky/ offensive/ innocuous/ whatever for this room/ these people... They'll hate it."
    Yet if I truly think it's funny, I have to take the chance and say it. You'd be shocked how often these are the things that get the biggest laugh.
  5. DON'T: Worry that writing jokes is hard for you, which means you're not a "real" joke writer. WRITING JOKES IS HARD! I've met people whose brains seem to naturally think in jokes (like Jeff Ross), and I envy the hell out of them. Because for me and PLENTY of comedy writers I know, jokes are tough!
  6. DON'T: Get all jaded-comedy-person and stop laughing at other people's work because you think it'll make you more discriminating. It'll make you shut down, rigid and no fun and all the other comedy writers will complain about you when you're not in the room.
  7. DO: Be honest. When you're asked to write jokes for a performer, look at the topic they're addressing and ask yourself: "What's the absolute, most honest thing that could be said at this moment?" Start there.
    Vulnerability is good, fear is good, silly is good, all that id stuff is good.
  8. DON'T: Be honest. Instead, be a sarcastic 14-year-old prick who shits on everything. Let that little asshole loose for a while when you're writing. It's fun!
    Just don't let him run the rest of your life, or you'll end up dead/ in rehab.
  9. DON'T: Turn in a page of jokes with spelling errors, bad punctuation, etc. You get one shot to show the person you're writing for how the joke is supposed to go.
  10. DO: Go write stuff that will make me laugh really hard and marvel at how your mind works! Nothing is more precious than a great joke!
    Especially when - again - you're an old man like me, who's heard every joke! Thank you for asking me to write this list, I hope I didn't come off too unbearably pretentious! Now to go write jokes for Ira Glass, who is hosting Comedy Central's Roast of Sarah Vowell. Woo-hoo!