I was in a 'similar' stage 2 years ago. I grouped with 3 of my friends and started having conversations on a daily basis. All of us came from different background -tech, finance, marketing, research; but had the same start-up itch. We threw ideas on the wall, critiqued them, followed up with some research. Eventually we found our start-up idea which btw has evolved into something completely different in 2 years. So:
1. Form a core group
2. brainstorm, read, research
3. DO IT