How can I ensure I don't get blacklisted?

To expand on to Andrew's "#2 - Deliver relevant email"... I would use segmentation in order to deliver relevant messaging.

You can of course use information base on interest questions or even surveys your prospects have taken.

If you are using a marketing automation platform, combine your prospects' attributes with their site visit history. For example if consumer "A" keeps visiting your site and looking at product "X" more than twice in one week and downloaded a whitepaper - it maybe a good idea to add consumer "A" into a nurture program on product X.

All of the advice prior is sage like and absolutely accurate but I would like to state the obvious: if possible avoid growing your lists inorganically, e.g. renting/buying names. The results could be long lasting and destructive to your reputation and ability to deliver mail for a long period of time.

Although creating more engaging email is good and all of us marketers are competing for the limited minutes, seconds and dollars of our mutual consumers, actions like emailing users who have opted out, importing lists with unknown pedigrees and partnering with less than noble partners can lead to the kind of blacklisting that could be very costly in the near and long run.

"How can I ensure I don't get blacklisted?"

Simply... you can't. Regardless of what you do, someone will blacklist you. In fact, I've already blacklisted you. Five-ten has probably already blacklisted you. If SORBS hasn't blacklisted you yet, they probably will soon.

But that's the wrong question. The real question is "how can I ensure my mail isn't blocked?". To do that you have to avoid being blacklisted by relevant public blacklists (of which there are no more than half a dozen or so) and also to avoid being blocked by private ISP filtering or content-based filters (such as spamassassin and all it's enterprise spam filter friends).

There are some bits of advice that apply to most every sender that other people have touched on (send compelling content to people who want it, don't violate any technical standards, handle your bounces, FBLs and unsubscribes and so on), but there are usually many other things you can do to avoid getting blocked that are more specific to your business model and your recipient demographic. Talk to a decent email consultant about that.

Use a respected email service provider that maintains relationships with ISPs, and requires its customers to send only to opted in recipients.