For more details on brainstorming techniques, I read the relevant parts of Module 2. It explains some frameworks of how to do brainstorming and it is nice to know them.
There are many techniques I have been using in these frameworks. One of them is to relax. It is super hard to relax when I get stuck on project. Whenever I feel I am in stuck, I intentionally try to make myself relax, go for a walk, have a coffee and eat dessert, listen to music, exercise, etc, so that I can be free from the thing I get stuck and get some fresh air.