Theres not much to it really. If you live in the United States make sure you follow the can spam laws which are available online but its always good to consult with a lawyer about your legal options. As far as the actual optin mailing goes services like aweber will let you manage your optin subscribers and mailings and if you really want to build up your optin list you need to give your users a reason to hand over their email address. Stuff like a weekly or monthly newsletter, free tips, or discount offers for your product are great ways to get more subscribers.
Thanks for writing back! Here's what Im looking for. I have a good friend that wants to get going with affiliate marketing and instead of me sitting down with him and sharing all my knowledge I want to just buy him the best ebook(s) on how to both run a very responsive opt in list. Im sure there are some kickbutt ebooks that really drive home some cool tips and tricks to get the most out of your list. From the very start where you collect them and how best to keep them active and buying. What product would you recommend that I buy for him?
Two words....and an initial....Jimmy D. Brown. I write about him on my blog all the time. I'm a member at his List and Traffic site (I have an affiliate link but I won't post it here cause I hate when people do that). I'm always amazed with the ideas he has, and he has a cool way of explaining it that always gets my brain exploding with even more ideas. List and Traffic is mainly about getting opt-ins and making the most out of them. I definitely recommend it. It's not an ebook though, it's a membership site you pay $10 a month for. He's also got plenty of other ebooks though, like 21 inbox tips, stuff like that. He gives his L&T members a deal on them, so I'm not sure what the full price is on most of them.