Hi
No one offers any magic formula and it depends on lots of things besides kw popularity and competing pages BUT this thread has the most helpful info and gives a variety of opinions/guidelines. From what I remember that video was pretty good, so watch it too.
Need help with SEO numbers - KeyWord Popularity vs Competing Pages?
We get this question a lot and I know it's one of the hardest things to figure out when you are new and trying to find a niche.
So I made that thread a sticky in hopes we can get members to keep adding tips and tricks.