Edit the Old post with Related Content:
If you edit old post with new related content and new idea then reader will read it with interest. New and relevant content also will give new life to your old content/blog. When you re write any content or edit your content of old post then visitor will again read it they would not feel boring.
So try to edit the post with related new content to keep old blog Alive.
Share post in Social Network:
Share post in any social media network such as Google Plus, Facebook, Tweeter. When you share any post it reach different types of group, they read this posts and share it.
The same process you can apply for older posts. I think you have gathered a lot of new followers since you last posted. So these new followers have never seen of your best post. You can again share you old post through above mention social media network, so that you can gain more traffic and keep your old blog post alive.
Tweet Old Post Plugin:
In case for WordPress you can rotate your old post through Tweet old post plugin. By this plugin you can customize your posts. You can select criteria, category by it. You can also set the time between two tweets and chose other option to customize the settings, as you want.
Link Old Post to New Post:
Internal link is an very important factor of any blog posts. It help to increase SEO (Search Engine optimization). You can put internal link with related article. Even you can connect any old post with related article by this internal link. So we can keep any old blog post alive by this internal link.
Update Related Image:
You can add new related image with new alt tag in old post which will help to get new information of related posts through Google Search Engine. Moreover any one can enter thats old topic through Google image search. So update old posts with new related images for better SEO rank.
Edit Old Blog Title:
Edit your old blog title with related word so that it looks like new and more sweet able to the reader. Changing the title will surely not mess up the SEO on your site as this will not change the permalink of your post.In this process only display title will be changed and this display title will be picked up as new information by Google Search engine.
Related Post Widget:
Generally we write blog many blog posts with similar topics, like if you are writing about gadgets there may be many posts on the gadgets category. So related post works based on the category, tag and content of your post, if your content matches with any of your older posts then the post shows in the list of related post widget, related post is
must for every blog, it always help to keep your old blog post alive.