Getting a lead's email address is just the mailing list beginning of a process of relationship and trust building that you need to engage in before you try to collect anyone's money. You build that relationship and trust through repeated contact via email. What should these follow up messages look like? Well, first of all, lucky for us, a lot of this has already been figured out.
There really is no need to run out and re-invent the wheel. I learned pretty much all I know about list building from "someone" else. Unless you're eager to spend a lot of time and money experimenting, you too should learn list building from mailing list someone who has clearly succeeded with that process. My list building mentor taught me a few basic things about writing effective follow up messages to a list.
The first and possibly the most important thing you need to do is write like you speak. Sounds pretty simple, right? Normal, informal, conversational writing is the most effective way to connect with your leads. Don't try to fool them - it won't work. Honest mailing list value is the only thing that you can provide to your list if you expect your leads to trust you enough to spend money.