A blog is more than just a sidebar jam packed with links. At its core, a blog is about writing & reading. Understanding what makes good typography is a skill you must acquire - if you care about your readers.
The font(s) you choose, the line height of the text along with a line length all contribute to or detract from your readers ability to comfortably read your writing. This is referred to as Readability - and it's an important step in setting up your blog.
Learning about typography and the effects of these different settings could take a long time - but, it doesn't have to ... enter the Interactive Guide to Blog Typography by Tommi Kaikkonen. Spending just a few minutes playing with this guide will show you how font size, line height and line length can effect the readability of your pages.