Heading Tags, <h>
You can use headings like h1, h2..... h6 to tell what the contents are. There should be a hierarchy. If your blog is using h1 for blog header, h2 for post header, consistently throughout the blog, search engines can understand what are blog, post headings and subheadings. I use, h1 for Blog heading, h2 for Post Heading, h3 for post subheading, h4 for comment heading and h5 for sidebar heading. Most Important are h1, h2 & h3 which if nested properly gets indexed by search engines.
Paragraph tag, <p>
Paragraphs wrapped in <p>....</p> are good for seo. It is considered the most important tags wrapping texts. Since, most texts on web are wrapped within this tag, search engines look out for them. You must use them in all your posts, to mark the paragraph, start and end.
Emphasis <em> & Strong <strong>
Many people don't know, <u>...</u> and <b>....</b> are obsolete tags. Use <em>...</em> to emphasize some text & <strong>.....</strong> to make it appear bold. The text within these tags are given due weightage by Search bots.
Use of Section Tag, <section>
There has been great debate on its usage. There are more Don'ts than Do's. Important point to remember are, it should have an embedded <h> tag, and content shouldn't be meant for syndication. As per my understanding, it is meant for article's bullet points in a box or table of content or some standalone information embedded within an article which might be of interest and importance to the reader, but are not meant for syndication. A kind of extra information not to be confused with main article body. It is meant for telling the search bots that the piece of information is, though related to the article is not its part. Use it in that way.
Theme Break <hr>
This horizontal rule tag is of historical importance for applying horizontal styling, but now, it has acquired a new meaning. It means theme break! Whenever, you apply <hr>...</hr> or self closing, <hr/>, it means the content after and before are of two different themes. What is of interest to search engines here is that, they may start sniffing of themes and information around them. It has been learnt its usage brings indexing enhancements.
5 Powerful HTML Tags for content SEO of Website or blog!
Following Tags will help Your Content catch the attention of Search Engines, in a Faster and Better way: