Working words: How to write for SEO

I often fill these pages with rants about what not to do when writing copy for search engine optimisation (SEO) and for a web audience.
However, it struck me recently that I have not spent much time exploring best practice in SEO copywriting and how to ensure your content is as fit for purpose as possible.
I am going to remedy that today. Please comment if you have any questions or additions.
Spiders
Spiders are the crawlers sent out by search engines such as Google to trawl through the web, recording details and information about the pages they visit.
What they find determines how well you rank for the words and terms within your site. So, what can you do to help?
1) Choose your keywords and phrases and stay conscious of them to ensure they appear whenever naturally possible within the website's text.
2) Spiders pay more attention to bold and italic words, so when you use such formatting, try to make sure it is a keyword or phrase.
3) They read left to right, so place your keywords as early as possible in the text.
4) Spiders consider headlines and sub headings to be particularly important, so make sure they are as relevant as possible and, if natural and readable, contain your keywords.
Humans
I am often amazed at how many people forget the real purpose of SEO. The motive is not to get to the top of the search engine results pages, not really. That is like saying the purpose of cooking is to heat meat, rather than eat it.
The idea is to gain greater visibility and traffic. That means all content on a page must be interesting to people. People, not search engines.
So, make your copy fun, interesting, relevant, grammatical. Everything a real person looks for when browsing the web. Also, try these tips:
1) Alliteration is good. Humans like alliterative phrasing and looking out for such opportunities allows the writer to concentrate on creating elegant copy rather than just functional words.
2) Use short sentences. The online reader is lazy. To help them read the page more easily, keep sentences short and try to limit paragraphs to just two or three lines.
3) Keep a sense of humour. Unless your pages cover genocide throughout history, there will be opportunities to make the odd joke. Seize these. The more personality you have on your site, the better.
4) Call to action. Your copy does not just exist for the reader to read, you are trying to secure business. While your content should not be one endless pitch, do not be afraid to include a call to action somewhere in it.
Linking out
There is a lot of confusion out there over links. Most people are happy with the basics: inbound links good, farmed links bad and so on, but some people worry that linking out from your content could devalue your site.
I believe there are three important points here.
1) If you are a human reading a website, outbound links to sources provide credibility and relevant further information. That makes you happy and gives you a positive impression of the page.
2) Should a search engine spider be looking at your content, outbound links to relevant pages are no problem, it will only get suspicious if you are linking out all the time and to irrelevant places.
This will devalue your site's importance to the search engines and, of course, too many links can make you look very suspicious.
3) If you want to link to a new pages, make sure a new window opens up. The last thing you want to be doing is directing people away from your site.
Linking in
Inbound links are brilliant; the more the better, particularly if you can receive them from high authority pages.
However, the main way to secure these links is to create impressive content that real people will want to link to.
This means good copywriting can result in good SEO. Rubbish and repetitive content may be cheaper or easier but it will not provide the long-term benefits you need.
Quality is everything
If you can't write, don't. If you can, then make sure you take the time to really hone your copy and make it as good as it can be.
Each time a company commits words to its pages, it is presenting itself to a potentially huge audience.
This might be the page that scores hugely in Digg or Sphinn and carries your firm's name around the world. Or, it might be that just one person sees it but he or she carries enormous buying power.
Make your words impress the search engines and the online community. Make your words work.