1. Traffic - the more, the better. I am talking about targeted and diverse (coming from different sources).
2. Lead Magnet - the freebie you are planning to offer. And the stakes are high these days; you'd better make it good.
3. Opt-in Form - eye-catching, to the point, and here's the tricky part: everywhere, but not intrusive.
3. Monetization - how are you planning on making money off your list. Your own product, services, affiliate products, etc.