It is proper Netiquette to write about one topic per post. Don’t write about several subjects.
Topic Netiquette Blogging
Multiple topics makes a post hard to follow. One subject per post helps you build an audience and a brand because your audience will expect one subject per post.
Topics and subjects should be consistent because blogs have world wide exposure. The exposure the world wide web provides requires specialized posts to overcome personal preferences and language barriers. Using a topic as a theme, a subject as a thesis and issues as example is a good format for any blog.
The topic issue and example can be a broad or specific as the author wants. By consistently writing about a particular topic or theme readers will be able to understand the reasoning because they understand the issue.
Write about one topic per post because it makes the meaning clear.