As my friend Nicolas suggested, I decided to give some guidelines and pointers about SEO (Search Engine Optimization). Now, full disclamer: I'm not a SEO expert, so what I am going to write is just very basic rules.
Also, since Google is by far the most popular search engine, I will focus on it. I assume visibility on Google is the most important for most webmasters. Anyway, what is valid for Google is usually valid for other search engines as well.
The reason why Google is so successful is that they managed to be smarter than shady webmasters who tricked search engines. With old search engines you could put 50 times the word "notebook" in a comment to get a decent placement on the search for "notebook", and you could also hide "Pamela Anderson" in a completely unrelated website to get some visits. Google, with their pagerank and smarter analysis of pages, created better search results for users.
That's what they are good at, and that's why they make so much money. So you can bet they're spending a lot of money and energy keeping this edge on unethical webmasters. I won't get into details but there are tricks such as cloaking, link farming, page hijacking... You don't want to use these techniques.
In short, you should play by the rules if you don't want to get punished. Read Google's webmaster guidelines. When you are done, you can also use their webmaster tools to check your website and create a sitemap.
Corollary: don't hire a SEO consultant who would use shady techniques.
It may sound obvious, but you can't just generate some crappy pages automatically and expect search engines to index it well. Some people do that by shamelessly sucking content from blogs, but it doesn't work.
Make sure your site is useful for real, human visitors. Also make sure that pages in itself are useful, that a user can jump in the middle of your site and get what he wants.
Search engine spiders don't see pages like human do: they only understand plain text. That means:
The pagerank is a metric introduced by Google to measure the popularity of a page. It's a number between 0 and 10. The inbound links you have, the highest this number is. If pages with a high pagerank link to your page, you get more "pagerank juice" and your pagerank is even higher.
Additionally, Google prefers inbound links from pages that are in the same category as yours. For example, a page about computer programming will benefit from links from other computer programming related pages, but not so much from pages about breeding dogs.
That means that you should develop your network - get in contact with people who have similar pages, make sure they know yours and that they link to you when it makes sense for their users.
For your website internally, that page rank system also works. A given page that gets popular may get a good pagerank, and your whole site must be architectured in a way that will redistribute the pagerank to other pages. That means not having more pages than necessary; if you do have too many pages (for example content broken into 5 pages when it would make sense to be one, or dynamic pages that don't give much more information), your pagerank juice will be divided into those pages instead of channeled to the one page. So be careful when you think about what should be on its own page and what should be integrated to another one.
This section could go for over and over, so I'll just limit myself to the basics.
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