This is the single most important thing you can do to optimize your blog for search and drive more traffic. Imagine what you might type into Google to find your post and include it in the title of your blog post. Clear, descriptive titles aren't necessarily clever or fun, but they will get more people to your blog.
Title images with one or more words from your post title to increase the "relevance" of your post. This will help your blog index better against that term.