In terms of purpose, the sidebars are similar to blog pages in that they should display general information that you would want your reader to access at any time. The sidebars are also where you place your blog widgets. I'll get more into blog widgets in a later post.
Due to the fact that blog sidebars are right next to your blog text column, they are more visible than pages. Here are some basic things that I think are necessary to have in a blog column:
- At least one subscription method for a reader to follow your blog. Multiple is better. But if I had to pick just one, I would say having a "follow by email" option is the best. It's easy, people understand email and people usually read their email.
- Blog archive. This shows all of your older posts. It gives readers a place to browse your blog. More importantly, it shows your readers how active your blog is.
- Search this blog. I think it's a useful tool if people want to type in a particular keyword.
- About me (blog author). This isn't really necessary. But it's a nice touch. Makes it seem more personal.
If you are trying to promote something with your blog, the sidebars are a good place to have small announcements or pictures. But moderation in all things. I really believe that the actual blog text should be the primary focus. The more columns you add and the more stuff you add to columns, the more distracting it will be from the actual blog posts.