Starting with ideas is hard, because people immediately want to evaluate your idea.
It's easier to start a problem, and think about your relationship with it.
Is it a problem that you have? That your customers have? That exists in your community?
Many of you in this group are consultants, coaches, and online experts - so you have deep experience in solving specific problems for people.
When you have personal connection with the problem, it will see you through the challenge of finding a solution.
So instead of keeping an 'ideas book', keep a 'problems book', and write down the problems you encounter on a daily basis.