How does a blog move from good to better to best? By constant improvement. At regular intervals you must take a break from writing blog posts and give an objective assessment of your blog. Figure out the strengths and weaknesses of your blog, then figure out how you can increase the former and lessen the latter.
There are several different ways to look at your blog, and these are the most important ones:
Focus. Do the topics you write about match the general objectives of your blog? Are there categories or areas you might have overlooked so far? Can you handle writing about these new topics should you add them to your list?
Experience. Are your readers having difficulty reading your blog? Do they have trouble finding certain things, like archived posts or that feed subscription link? Do they understand what feeds are? Do you encourage them to leave comments? Do you react to their comments? Is it time to redesign your blog?
Promotion. How popular is your blog? Can other people find your blog through search engines? Who are linking to your blog? Do you link to others as well?
Start by answering these questions to yourself for each of your respective blogs, and then feel free to ask more. Never stop wondering what you can do to improve your blog.