Rule 1: never buy email list. Never pay others to send mails to their list unless you know the open rate of emails (which is usually terrible for people who rent out their email list to others for sending emails) and the persons audience and your purposes are aligned, which is a rare case. If you send emails about deals on smart phones to my email list of law students who signed up on my list to learn more about legal research, it is never going to work.
Wait, it works for the list owner you end up paying, but not for you or the email recipients.
Rule 2: Drive the traffic coming to your website to sign up for your email list. It can be a pop over or a box at the top right corner or a button inviting to subscribe. Offer something – a small report/ a download in exchange for signing up. I personally do not offer any such thing for my email lists – just an invitation to keep in touch seems to be working.
Rule 3: Send only relevant mails. Send them at regular intervals. Not too many at once. Always remember how easy it is for people to filter any mails these days – they don’t even need to unsubscribe.
Observation 1: We did some webinars and people had to sign up for an email list to participate. We found this to be quite handy as a tool to increase the size of our list.
Observation 2: Another great way to build a list in the long term is to start a community. My biggest email list is basically a ning website, just like this one.