Although the internet has changed a great deal in the last ten years, one thing that has remained status quo is the way that webmasters designate topics and things of importance. Topics of a page are often set with header tags <h1> though <h6>, while important items are put in bold to make sure that the user noticed them. However, not just the user notices these attention-grabbing tags. Search engines also use these as primary indicators of what a page is about and what content its creator thought was most important.

Header Tags - <h1> through <h6>

Header tags are a great way to help boost your search engine rankings. If you're creating a page about "free hats" and would like to rank for it, there's nothing shady at all about including a nice big <h1>Free Hats</h1> at the top of the page to make sure your users and the search engines know what your page's subject is. However, as with other search engine strategies, it is important not to stuff too many keywords into these tags. A good rule of thumb is to include no more than 3 or 4 <h1> tags per page, and always have at least a paragraph or two of text between your header tags.
A page that consists entirely of header tags looks pretty spammy to search engines, and it isn't very useful to your visitors.

Bold, Italic, and Emphasis

When you've used up your quota of header tags on the page, don't stress out. There are still plenty of tools to target your keywords with. When mentioning your keywords throughout the page, it's helpful to put them into italics, bold, or emphasis (<em>) to make sure the search engines know that these words are important.
Often people use a lot of flash animations and CSS <span> tags to format text, but search engines don't have an easy way of determining either of these. Why make the search engines work harder than they need to? Use these basic HTML tags and help yourself (and the engines) out!