1. Comics show up with lots of pieces of paper. If you can't show up to a comedy workshop with a pen and pieces of paper, you don't deserve to call yourself a comic and your family should be killed. Just a thought.
2. Everyone puts in the same number of topics, just to be fair. Three topics seems to work nicely. Keep your topic to a noun. No premise, no explanation. Not "The agony of a blind date" or "Thinking about standing up a blind date." -- No angles allowed! Topics with angles are too limited for improvization, and it's not fair to add extra burdens on people trying to help you with your joke by riffing on your topic. Just a noun or noun phrase, like "blind date."
3. Someone draws a topic at random. If they draw their own topic, they put it back. This is a self-enforcing law, as the topic owner has to acknowledge who they are to get the notes after the riff.
4. The drawer announces the topic. Everyone else takes a piece of paper and they write the topic on it. This encourages and reminds everyone that they have to give feedback if they expect to get feedback in return.
5. The drawer riffs on the topic onstage for a set amount of time. Timers are helpful. Everyone else can raise their hand with ideas for the riffer. Good questions to get the riffer out of a rut: "What's wierd about (topic)?" "What's stupid about (topic)?" "What's hard about (topic)?" "What's scary about (topic)?"
6. Everything everyone says and writes during the riff is the intellectual property of the topic owner. That's how workshopping works: we devote our brains to each other's problems so that everybody wins.
7. Don't admit the topic is yours until the riffer leaves the stage. This is to your advantage, because you'll get better feedback if people aren't thinking about who owns the topic. Admit ownership, then sweep the room for your notes. This encourages people to give you notes because they'll want notes from you when it's their turn to sweep the room for notes on their own topic.
8. If you think of something you want to keep, you can keep it to yourself, but you'd better write another brilliant idea on the paper if you want feedback in return.
9. Repeat until you run out of topics or everybody dies.