Ask What are the simple secrets for creating a successful membership site?

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I want to create a membership site but I have no idea where to start. Some sites seem to grow fast, while others fail. I don't know what makes the difference. Do I need a large audience first? Should I offer exclusive content or focus on a strong community? I also wonder how to keep people subscribed for the long term. I want to avoid common mistakes and do things right from the start.

What are the simple secrets for creating a successful membership site?