On the Usage of Header Tags
There are two main sapects to consider when styling your text. One aspect is your visitors, the other aspect are search engines.
There are lots of very different types of pages.
A informational page with lots of text, or a product page, with perhaps 3 lines of text and a product name, and a buy now line - those are different pages, and they need different use of header tags, and the <b> or <strong> tag.
So what you could do is make a document in word or another writing programme, or write it up on paper, and determine how you want it to look.
The Hierarchy of the Header Tags
The <h1> Tag
Try and have a <h1> header on top of the page. In that <h1> you write a short sentence containing the most important content. So if your page is about selling holidays on mars, your <h1> could read:"Holidays on Mars - a new experience!"
So with that you have defined for your visitors and the search engines what is the main topic of the page.
Subheaders, <h2>, <h3>
The numbers following the <h> in the header tags define a hirarchy. <h1> is the largest for most importance, <h6> is the least important and large header.
If you have more than one paragraph of text it makes good sense to give each paragraph a subheader, which does the same for the paragraph as what the <h1> header does for the whole page: Set the main topic of that paragraph.
For long texts you might find it useful to further structure your paragraphs by using a <h3> tag.
Small Subheaders, <h4>, <h5> <h6>
Those are rarely neccessary for text oriented pages. Especially so since there are other, more useful tags to structure long texts on webpages, for example the list building tags, or the emphasizing tags like <b> or <strong>.
A good usage of the small subheaders might be for extra blocks of information on a page, like navigation elements, or call to action areas.
Header Tags and Search Engine Ranking
Do Headers Influence Ranking?
The short answer to this question is yes. Of course all search engines use different ranking methods. But generally having the most important keywords in the header tags on a page helps ranking better for those keywords.
Can I Put Everything in Header Tags?
Putting all text on a page in header tags will very likely have an adverse effect on search engine rankings. Headers are a way to stress certain parts of the text to give it special importance. If all text is stressed, no part of it is of special importance anymore.
Conclusion: Do it Naturally!
The best way to use header tags on web pages is to set them for your human visitors. Try to reach out to them with your text layout. Make sure they get to know fast what your page is about. Stress the important parts, but don't yell at them by stressing too much.
By that approach you will also get the best out of your header tags for your ranking in search engines.