What kind of brainstorming works varies a lot from person to person.
Here are some examples.
1-Some prefer to write as many ideas in a piece of paper during a few minutes.
2-Others prefer to suggest ideas to each other as a team
3-Or maybe starting with a question?
4-Setting cards with words and draw one randomly and think what ideas come with that word
Curiously the one that worked for me is asking myself a question about the plot of my comic or a joke, then i roll a dice, if i roll an even number is a "yes" and odd numbers are a "no". Then i ask myself why the "yes" or "no" is an apropiare answer for my story.
You must see what works for you.