Remember last post where I suggested how you could extend a post in numerous ways including by answering a question that a reader asked about it in comments, taking an opposite view point, writing an opinion piece, doing a followup ‘how to’ etc.
Get a whiteboard, piece of paper, note book, tablet pc or something else to write on (there are also various mind mapping tools and software options out there - but I find a pen and paper can work just fine) and draw five circles across the middle of the page. In each circle write the titles of the last five posts on your blog (if you want to do this more comprehensively go back further and do it with more posts).
Now take each post in turn and spend a few minutes brainstorming on ways that the post could be extended. For each idea draw a line out from the circle, draw a square (or use a different color) and write the idea inside of it.