When writing about controversial television advertising, how do start to brainstorm?

I have to write a persuasive essay on controversial television advertising. I have read some of the ideas and they all great; however, I am not good at brainstorming. I'm either overthinking or underthinking my ideas. Can some please tell me how I can get started without my mind going blank? And how do you narrow down your ideas?

Individual Brainstorming

When you brainstorm on your own you will tend to produce a wider range of ideas than with group brainstorming - you do not have to worry about other people's egos or opinions, and can therefore be more freely creative. You may not, however, develop ideas as effectively as you do not have the experience of a group to help you.

Ust the tool call mind map. Find it on google

When Brainstorming on your own, it can be helpful to use Mind Maps to arrange and develop ideas.

Group Brainstorming ideas in more depth than individual brainstorming.

Write down some commercials you have seen that you think are controversial and then make a plan of what you are going to do,like write what paragraph is going to be about.