What brought you two together? Why do you think you'd be good partners?
Maybe examining your cross-over of interests, abilities, knowledge, etc. will make something pop out.
Just start building SOMETHING. Give it a go, come up with a tiny idea and see what comes from it. Without knowing your abilities, etc. it's tough to know what your areas of interest may be.
We knew each other from startup meetup groups ~2 years ago, kept short contact over the last 2 years, and this month reunited and have been talking about ideas since.
We'd be good, because we have complimentary skill sets, and personalities.
The most valuable idea you can work on, and the one most likely to succeed, is one you are scared of. An idea you won't admit to yourself.
So one approach to finding that idea is to try hard to not come up with an idea. Make that a goal and you may notice that ideas start flowing in that way. Individually, write down these urges, and focus on summoning the courage to face them.
Maybe examining your cross-over of interests, abilities, knowledge, etc. will make something pop out.
Just start building SOMETHING. Give it a go, come up with a tiny idea and see what comes from it. Without knowing your abilities, etc. it's tough to know what your areas of interest may be.