I use my list to send out occasional offers and freebies that aren't available elsewhere. For example in the last 2 months I sent out a special wordpress discount for the Easy Azon plugin that earned me a nice chunk of affiliate change and an ebook on SEO. The idea is to also provide exclusive value that you don't provide on your site.
When I first started an email list I had no clue what to do but I learned you need to have a strategy from the beginning and more importantly communicate that strategy upfront. So for example as soon as someone subscribes I remind them (via autoresponder) what they are going to receive and how there will be exclusive tips that you won't find on my site.
Setting that expectation is key because people will get an idea for how often they can expect to hear from you. And if you use it to send out your blog posts like I do, make sure they know that there are other benefits to being on your list.
Communicating that exclusive value up front is key. This is something I did not do in the beginning. I just collected emails and wasn't really sure how I was going to use them. I would send out stuff sporadically and because it was so inconsistent my open rates were terrible. Now they have improved tremendously because I send regularly and offer occasional exclusive offeres/freebies.