To get higher rank in SERPs.

The below factors and techniques are not as crucial as the ones described above, but still they help a bit in gaining a higher rank in SERPs.

1. Headings
   Once upon a time search engines paid a close attention to the heading tags (H1 through H6), but now those days are gone. Heading tags are easily manipulated, so their value is not very high nowadays. Nevertheless, you still want to use headings to mark the beginning of a text, to split an article into parts, to organize sections and sub-sections within your document. In other words, despite headers provide merely a small SEO value, they are still crucial for making your texts easiliy readable by human visitors.
   
   Use the H1 tag for the main heading of the page, then the H2 for the article headings and the H3 to split the different parts of an article with sub-headers. That would be pretty good practice and is enough to make your site readable by humans. It also adds some SEO points which you should not neglect too.
2. Bold/Strong and Italic/Emphasized text
   Both are nearly useless, but still have some SEO value (very little though). As with headers, you better use them for the benefit of your human visitors, emphasizing the key parts of the text. But do not put every 5th keyword in a bold text as it looks ugly while not giving any significant boost to your rankings anyway. Moreover, such page would be very hard to read.
3. Keyword placement
   The value of keywords in a text depends on their placement across the page. Keywords placed near the top of the document get higher value than ones residing near the bottom. Important: when I say top or bottom I mean the source of the HTML document, not its visual appearance. That is why you want to put your navigation and supplemental texts near the bottom of the source file and all important and relevant content - near the top.
   
   This rule also works in more specific cases: keywords placed in the beginning of the title tag are more important than ones placed 4th or 5th. Keywords placed in the beginning of the anchor text are more important and get more value too.
4. Keywords in filenames and domain name
   An old trick with putting your target keywords into a filename or having them in a domain name. Still works, but don't expect too much boost from this one.

a) Keywords in a domain name do help a little, but it is much better to have a short, easy to remember domain name than something like www.all-of-my-target-keywords-i-so-much-want-to-rank-for.com

b) Keywords in a file or a folder name also help a bit and since you still want to name your documents, why not give them appropriate names? Though as I said before, do not expect any significant ranking boost. For a competitive query it won't help you much anyway. Also, if your page is written in other language than default English (or some other european language), it won't help you at all.

5. Image Alt attribute
   This one was very popular in 2003, but now keyword stuffing of the Alt attribute does not give any SEO value to a page. The better use of the Alt attribute would be something like this: alt="accurate description of some pic">
   
   Write a natural description for each image and make sure it reads well. This helps you in two ways: a) your site ranks better in the image search; b) Google often takes the Alt text to create a snippet for the SERP.
6. Meta Description
   One of the most popular and steady myths (alongside with keyword density) is the Meta Description tag. They say it helps you rank better. They say it is crucial to have it filled with the apropriate description of a page content. They say you must have it on each page of your website. All of these is not true. Nowadays, the only way the Meta Description is used by search engines is taking its content to create a snippet for the SERP. That is all! You don't get any other benefits of using the Meta D on your page, neither do you fall upon any penalty for not using it.
   
   There is an opposite opinion suggesting not to use the Meta D at all, since a search engine anyway creates a snippet basing on the content of a page and you can't make this work better than a search engine. So why waste your time doing that? Personally, I would not agree with this point, since according to google guidelines the Meta Description tag is still the preferred source of the info for a snippet. Though it is up to you decide whether you want it on your page or not, since as stated above it doesn't give any additional SEO impact, neither positive, nor negative.