Chris Lema shared a lot of good advice (as you may expect!) in an AMA on ManageWP.
Chris always has a nice post on what plugin developers sometimes forget, based on his experience reviewing a ton of membership plugins:
What if the real risk is that your plugin functions but doesn’t get traction because users feel like it’s too complicated? What if the real challenge is that you’ve created a technically competent solution that has no empathy for its intended user?