search engine robot reads your content just the way a human reads it. Headlines, bolded and highlighted texts draw attention. By default all blogger templates are designed such that the H1 tag is given to Homepage Main Title, H2 is given to Blog Description or Header dates, sidebar headers and H3 is assigned for post titles. Whilst the fact is that your Post titles are second most important part of your blog after the main title. Sidebar titles and Post description are peanuts in comparison to your post titles.
Changing Post Tiles Heading Tags In Blogger:To change post titles default H3 tag to H2 heading Tag then follow the steps below,
<h3><data:title/></h3and replace it with this,
<h2><data:title/></h2>6. Save your template