The H1 tag is very most and required heading tag to a page or post of a Website or Blog. Each page or a post must contain at least one H1 tag, otherwise, you are not helping your users in differentiating content and title of the post.

IMPORTANCE OF H1 TAG FOR A WEBSITE OR BLOGGER

Normally h1 tag has to be used with the title. But most of the WordPress themes and Blogger templates do not follow this criterion. As of my experience with Blogger templates, the H2 tag is used emphasize a post/page title. You need to change that to h1 or otherwise, you are not making your post Search Engine Friendly. Let me first discuss the following questions.
1. What is H1 Tag and Why is it required?
2. How to use H1 tag?
3. Advantages of using!

What is H1 Tag and Why is it required?

A title provided with each post or page is called Heading. People who are familiar with HTML does know that there are a total of 6 heading tags and each has their own importance. We have H1, H2, H3, H4, H5 and H6 tags under the heading category. Using them appropriately is required for making a post Search Engine friendly. A title of the post (denoted with heading tags) helps the user in finding the main idea of a post and also to differentiate it from rest of the content.

Of all the available heading tags h1 is used at least once and not more than that because only 1 title is given to a post and in visual it is the largest and thickest of all others. The other tags are used to denote sub-heading and some other parts of post content. A title should define the content beneath it. So visually it is important to help the user in finding the title of the post easily, to these requirements only h1 tag meets our expectations.

That is why h1 is recommended to use with the title and not other parts of a page. Not more than one h1 has to be used for each page/post because we only provide a single title and it should emphasize the content in it. For example, while reading a textbook you can always see the Unit title or Chapter is different from the rest of the content in that chapter/unit. The same way title differentiates a post from the rest of its. content

How to use H1 tag?

As you know h1 only has to be used with the title and not to any other parts of a page. If you take Blogger templates, the name of the site (eg: my title is TECHAPU) is denoted with h1 tag and when you use the h1 tag with a post then you will have 2 h1 tags in them. So you need to change site name from h1 to h2, can continue to use h1 to denote title. For this, to work you need to edit the code of a template. To add h1 to the title first Inspect it from developer tools and go to that respective code, change h2 to h1.

Wordpress users also have to change only if not provided by your theme provider. Through Inspect Element you can find which heading tag was used with title and change accordingly in your template code.

If you want to verify how many h1 tags are present in your site then you can use some SEO Tools or Bing Webmaster (recommended). The way you use other heading tags is also important. Because for sub-heading and sub-sub-heading you always have to use other heading tags except for h1. You should not use <em> or <strong> with heading and sub-heading.  Remember only h1 tag is allowed either it is home page or post or static page. You already know how to write the title of the post so I need not tell how to use h1 effectively.

Advantages of using it

1. Helps for rankings in Bing Webmaster. If you are using Bing Webmaster (submitted website to it) then it always asks you to maintain one h1 tag per page or post. If you want to verify go to SEO Reports present under Reports and Data. It specifies every error your site is having. For verifying a single post or page use SEO Analyzer present under Diagnostics and Tools. It asks for a URL, provides it and click on Analyze and within few seconds you will see the errors for the specified URL.
2. Highlights from rest of the content and helps user to find it easily.
3. Specifies content of the post.
4. On using h1 it makes that page/post Search Engine friendly.
5. May change your rankings (not always).

Avoid (usage of h* tags):

1. You should not use <em> and <strong> with headings and sub-headings.
2. Length of text heading tags should be between 10-70
3. Do not overuse heading tags.
4. Use them appropriately when needed

That is it. Remember only h1 tag has to be used and it has to be associated with the title of the page or post. The way you are using title applies to h1 means whatever ways or methods that you apply on title need not be changed.