I claim myself to be a relatively good and fast developer, with the ability and experience in many various technologies from full stack web to mobile to embedded.

Yet I always have the issue of not knowing what to build, especially when it comes to a SaaS. I can never come up with a proper idea that could actually gain any users, let alone generate any money, and when I do, I never know how to actually gain those users or advertise.

Could anyone guide me on how to actually learn to build SaaS projects?