I would recommend finding an existing market. By that find something that already exists and has paying customers. If they have hundreds of reviews or if there is a forum where the product or service is actively discussed go there. Look for one or two common problems that paying customers have that is not being addressed. Try to make a product that is similar but solves those one or two problems.

Then work your way nicely into the forum and be helpful. Only after some time, suggest your product as a solution.