Here are a few guidelines for making your blog 100% usable, along with some observations on how users dealt with blogs in tests.
1. Make archives visible and accessible
Many users ignored or didn't see the archive links in the margin of a blog, even when asked to perform tasks that clearly required reading older posts. In addition to making sure the archives are accessible, also consider a list of "greatest hits" (say, your most popular or important posts) for users not interested in plowing through archives.
2. Indicate when images are clickable
Users didn't realize that several images were hyperlinks either to larger images or more information about the image.
3. Provide author's bio
When asked to evaluate the quality and trustworthiness of a blog, users consistently attempt to find who's behind it. When this information wasn't immediately visible, users wasted time digging for it. So be sure to provide at least a brief introduction (you can fit it on the homepage). Telling people more about you also provides useful context: "Is this person likely to know the answer to my question? Should I keep digging here or turn around (i.e. back button to Google) and try another site?"
4. Avoid blog jargon
Get used to the reality that many readers worth having still don't know what a blog is, never mind a permalink. Consider a more descriptive name for your blog, or just your name. You can still use the word "blog," but it's best to support it with another name.5. Don't use tiny type.
This one may seem out of place because it applies to all websites, but it came up repeatedly when testing blogs. You're not winning any coolness points with small type, but you're probably losing a few users. Just make it readable--so what if the page has to be a bit longer?
The guidelines above will seem obvious to experienced bloggers and frequent readers of blogs. But they are significant if you want to make your blog fully accessible to a wider audience, or if you'd like your users to take advantage of the whole blog, not just read your latest few posts.