There are many ways to create a membership site, so the niche area has to be thought out plus lots of content must be added regularly for members to stick around, but overall the most important factor of a membership site is how you are gong to monetize it to your advantage.
Is your membership site going to be a free membership site that monetizes with relevant advertising catered to your members?
Or are you going to create a paid membership site, were you get paid every single month from each member you have, which creates residual income?
Whatever the case you have to research and find aswell as create great content that will keep your members coming back to your site and paying the monthly fee or just hang around as a free member reading and enjoying your targeted content.
The membership millionaire is a free to join site were you will find out how to run your own membership site and there are 10 course modules to study, aswell as put what you learn into practice.