There are a few different ways to brainstorm, but the most important thing is to just get started and get all of your ideas out there. Once you have all of your ideas down, you can start to organize and prioritize them.
One way to brainstorm is to just start writing down whatever comes to mind. Don't worry about if it's a good idea or not, just get it down. Once you have everything down, you can start to sift through and see what's worth pursuing.
Another way to brainstorm is to use a Mind Map. Draw a big circle in the middle of a piece of paper and write your main idea in the middle. Then, draw branches off of that main idea and write related ideas on those branches. This can help you to see all of your ideas in one place and start to see how they all fit together.
You can also try brainstorming with a group. This can be a great way to get fresh perspectives on your ideas and to get feedback and input from others.
Whatever method you use, the most important thing is to just get started and get all of your ideas out there. Once you have everything down, you can start to sift through and see what's worth pursuing.