Another idea is to repurpose your old content into fresh, new content. If you've got a series of related, older posts, consider putting those into some sort of downloadable pdf (in exchange for email ) that your readers can take with them and then link to the old posts in that PDF.

If you're creating a 'how-to' guide and using older posts as some of the content, make sure to link directly to those posts in the PDF. Head over to http://blog.hubspot.com/ for awesome examples of this in production.

Assuming you're running WordPress, you should explore the plugin called Insights from Vladimir Prelovac ( http://www.prelovac.com/vladimir/wordpress-plugins/insights ) to help you connect with older content and media, as well as SEO Smart Links ( http://www.prelovac.com/vladimir/wordpress-plugins/seo-smart-links ) to help you automatically interlink older posts.

A third option is to fire up Adwords and build a campaign around your old posts. If you're doing this, then ensure that you're funneling those paid-for clicks from Google > Old Posts > call to action to New Post / Subscriber. Capturing new visitors and showing them your great archived posts, then pushing them to new ones has been quite effective for our customers and encouraging engagement.