Category plays an important role to search engines as well as readers. Readers tend to search articles under a category that they have interest. Poorly organized categories can not bring any good value to the blog owner, as it may not place any good value to increase the page views.
How to Organize Category?
1. Plan categories before starting
Before you start a blog, it is wise to plan your categories. You should have some research and note down some categories which matches the content of your site. If you start writing on certain categories and later decide not to write on some of those categories, then those categories will not tend to attract visitors for not having new contents. So it is wise to have some planning on categories before you write.
2. Limit total number of categories
Limit the total number of categories, because the less the number of categories, the more there will be total number of posts under each category. Say if you have 300 posts and 15 categories, then average post per category is 20. If you have less and organized categories, this will bring good values to your readers. New categories should be created rarely and only when it is necessary.
3. Make all categories navigational from homepage
Some people create additional categories while they write and those categories cannot be accessed from homepage. Simply there is no direct link by which user can reach into those categories. Posts on those categories can generally be accessed through related posts/popular posts but no direct navigation. But to make the readers and search engines both to find your pages, you should have linking to those categories through your navigation.
4. Categories should be noindex for better SEO
Categories and tags can create post duplication issue, as the same post can be accessed through homepage, categories and tags. So it is wise to make your categories and tags as noindex but dofollow. Some themes like Thesis, Genesis and other some premium themes have built-in option to configure the indexing tag, but if your theme do not has such option, you can download Robots Meta and can configure the settings. Though this plugin has not updated for long, still it is popular and worthy for your needs.
5. Assign only one category for each post
Some people tends to assign one post to multiple categories to make it more visible to the readers. But this can cause post duplication issues as well as increase the chance to bring the same post in front of your readers. Each posts should be assigned under one category, because say if you assign 2 categories for a new post, the post will be visible to your homepage as well as 1st category and 2nd category page and might confuse your regular readers who visit through the homepage.