Nurture your mailing list
This is such a big "Thing" that nearly qualifies as two "One Thing(s)". It was only after finally diving into the world of mailing lists that I started to see some steady income rather than dribbles of sporadic income.
My words of wisdom are to study it, earn everything your possibly can about creating and maintaining a mailing list. The most fundamental thing to remember is that people will sign up for free bonuses, but they will stay for valuable info.
I personally delete a tonne of unread emails each day but they few that I open are from marketers (or businesses) that I have come to KNOW will always have some good value in them - some new way of thinking about an age old problem, a report of free ebook attached to the email or just something that I know I will benefit from.
There is one particular marketer who includes a new joke in each email. His emails are a little hit & miss (sometimes I learn something, sometimes they're just affiliate links stuffed in between common sensical info) however I stay on the list because I know I need a laugh.
Emails with attachments are usually opened first. They might contain video's, pictures or an report, in any case, curiosity overcomes me. (Hint hint)
And that's kind of the point - whatever subject line you choose must be so enticing that the subscriber cannot resist but choose your email over the over 10, 50, 100 emails that find thier way into their Inbox each day. It is ESSENTIAL that you get the subject line right.
If you are too pushy, not pushy enough, if it reads like it's all hype, or isn't exciting enough...if you mention my Cb account, my PayPal account or several others...I'll delete you on the spot. In all fairness, the PayPal and Clickbank one's must be working because I've had HEAPS of them recently.
The timing of your emails is also an important factor that you will need to research on your own. Sending emails in that first week while the recipient is still on a high from the product they purchased or the freebie from your squeeze page is very effective. But be warned, the frequency of emails must be aligned with the niche to which you cater to. Sending Nana's emails about their health & wellbeing each day is going to constitute as spam in their eyes - just because we use the computer each day, doesn't mean your niche does.
Don't think of it as losing people when they unsubscribe. Perception is everything. You haven't lost a prospect...you've gained some data. There was a reason that person sent you a very clear message ("You aren't catering to my needs") but the question is how are you going to USE that data. If you look well enough, you might see that your unsub's have common demographics...so what could you change to make your email more appealing to those people?
Getting people to sign up is an art unto itself, most commonly aided by a free ebook or report. The more info you collect at this time, the more targeted your email campaigns can be. However (there's always a catch!), the less info you ask for, the more inclined people are to sign up. These days, a name and email is the norm but you can ask people to fill put public profiles etc later on.
There is so much to say about mailing lists - they are a great way to keep people updated about sales or services or just to sell follow on products - and not enough tie to say it all...
Get out there and learn it for yourself.