ANSWER: The secret to great email marketing is give more than you take. Give people a reason to love opening your emails.
Give them your best stuff for free. Load them up with everything they need to succeed. Demonstrate why you are the expert in the topic of the list and show them the way. Provide massive value with posts, ebooks, white papers, videos, tips tricks etc
Also be reliable (regular emails) and trustworthy. Never try to trick them or dupe them.
It also means you rarely sell to them on the list and when you do it should be a killer exclusive deal that has high value and low friction (easy to buy, money back guarantee).
The other smart thing to do is to use a Smart CRM system so you can track behaviour and engage with individuals when they demonstrate that they are ready to buy or engage. You can use a variety of platforms. Ontraport is one. We use the sales and email marketing software called Infusionsoft.