Use of highlighting HTML Elements
Specifically, I am referring to the use of Headings, Italics, Bold, and Link Anchors, which all contribute to SEO in that they signal a visual or functional highlight to the user, and therefore also to the Algorithm.
Use of Headings should follow these guidelines:
H1 should appear once in the page, and at or near the top of the page. It should contain keywords and be used sparingly, i.e. with not more than about 10 words within the tag.
H2 should appear at least once, but only to head a major subsection, or as a sub-title to H1. It should contain keywords and be used sparingly, i.e. with not more than about 10 words within the tag.
If the page consists of only one major section or 2 major subsections, use H2 only once for each. It can be used for more per section, but it’s unlikely that you’ll have more than 2 major subsections unless your copy is very long.
H3 should appear as many time as required to head a minor subsection. Subsections can also contain H4, H5 and H6 tags for minor headings.
Google will likely detect your H structure and also check the content within the structures. It’s commonly considered that H1 and H2 are signals for SEO
Here’s a view held by Rand Fishkin of MOZ – skip to point 10.
Apply keyword phrase fronting preferred or tailing if necessary for readability. The key to proper H tag use is to avoid using them as styling elements. If you wish to style sections of text to be similar in size to H tags, use a span class instead (CSS). This is a common mistake (in regard to SEO) that web developers make when building a site, and it’s an easy mistake to make. Usually the web developer is not the SEO, or does not perform any SEO work during web build.
The <em> element should mark any words within <p> that need to be emphasised to the reader. For SEO purposes, this should only be applied in the same way you would in offline texts, to stress a word or bring particular attention to it. Try to avoid using <em> if you are doing so solely for SEO, or when it doesn’t make sense within context. The ideal <em> element contains a fronted keyword phrase, or solely the keyword phrase.
The <p> element in the page should carry the bulk of the text, because this will be regarded as your main copy. Avoid using an H tag for copy. If your <p> style is not suitable, change the CSS settings for <p> until they are. If you want variation in your <p> styles (which I don’t recommend) you should define your alternate <p> styles in a new class, rather than use an inappropriate element like H. The <p> element should contain the majority of the text on your page. The <p> style also needs to be easily legible. I recommend using a px size of 15 or larger for your <p> elements. This is because font size is probably a factor in assessing text for rank, because a small font makes your text less legible for some readers – remember: what affects your reader in a negative or positive way is probably a ranking factor.
The <a> element defines an ‘active’ element – usually a link or anchor point. The link <a href=”URL”>anchor text</a> is used to refer users to a destination page. The anchor text within the link mostly affects the SEO value of the destination. If linking within your site, there is no problem with using commercially relevant anchor texts. In fact it is preferred, because that sends a clear signal to the user about the relevance of the destination page. Many web developers or website owners may use anchor texts like “click here” or “read more”. Those are OK too, but in moderation. There should probably be a natural distribution of such anchors within any site, balanced against keyword phrase anchors – as that would look most ‘natural’.
It’s less usual (but not problematic) for an <a href…> element to be inside an H element.
Styling of <a> elements should be done in a way that the user can identify it as a link without having to hover over it. In other words, if your user can’t see that some text is linked, then this might count against you for rank assessment, because you are effectively hiding the link. Typical styling for <a> elements is an underline or different colour than the element it’s within, so that they are easily spotted by the user. This site uses the colour difference strategy as I happen to dislike underlines, not for any other SEO reason. Adding links into a site that are completely hidden from view, by way of background blending, tiny font size or far off-page scroll location is a no-no. Such link use will probably attract a negative score for SEO.