with these sorts of things, it helps to perform structured brainstorming where you are generating ideas into different idea buckets that give you full coverage for what you are trying to do. This is easier than just listing ideas in random order off of the top of your head, and it also makes communication much easier.
If you are already doing this and just getting to the point where you hit a roadblock in idea generation, it can honestly be tough. Try to think of analogous situations, pull from real industry examples you know of, etc. If you are more interested in the topic, google for "creativity techniques" - academia has come up with numerous techniques for better idea generation.
Also, McKinsey published an interesting article on steps to perform better brainstorming accessible via:
Good luck! :)