Here is what I think:
First of all, start with a quick
keyword research. Don't waste too much time on it, but it gives you ideas of what people search.
Once you've made a list of keywords, integrate them to:
- the
Title attribute. One of the most important thing to optimize. Don't put too much keywords there. Again, make it user friendly.
-
Description tag. As you said, one page = one description. Don't stuff them with keywords as it is the text that usually appears under your link in the SERPs. (some SEs show your DMOZ description text) you can prevent that by using <META NAME="ROBOTS" CONTENT="NOODP">
-keyword tag. Pretty much ignored by much SEs. It's still good practice to put one as some SEs still look at it but don't waste time on it.
-
alt attribute: when you insert an image, make sure to describe the alt attribute so that the SE's know what your image is about.
-
Header tags Set up hierarchy in your titles naming them H1 - H2 etc...the words in those title have more weight according to SEs.
- Content: Don't worry about keyword density etc....write for the
users, not for the search engines, but try to add relevant keywords in it if possible. The thing is, some people say that if the overall keyword density is higher than 15/20%, you might get penalized. My point is: your content will look like crap and no one will stay on your website.
Keyword in bold and close to the top supposedly have a little more weight than other but if you start thinking this way, you'll end up with a big migraine.
-
links: use keywords in the anchor text of the links. (precision: I'm talking about internal links as "links are advertising, not optimizing

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Navigation: you should be able to access every page of your website within two clicks. You can create a sitemap and submit it to SEs to help them find all your pages (for big websites). You can prevent SEs to index some pages.
Here is a link to
Google's list on what tag they read and which one they don't care about
A common mistake: having URL Variants of the same page, for example:
http://www domain com
http://domain com
http://www domain com/index.htm
http:/domain com/index.htm
etc...If you do that, SEs think all those pages are different. Set up a 301 redirect to only one of them (I would recommend
http://www domain com even if it doesn't matter) to stop splitting your SEO efforts between different pages.
I will say it here to prevent 50 spam comments: (if only)
build more links.
Try to build
relevant links that will drive targeted traffic to your website, with keyword in the anchor text of the link.
For example: "chicken for sale" would be a better link than: www chicken com
Add a blog to your website and keep on posting relevant content on it. SEs love it and will come index your website often.
Don't worry about SE submission or directory/social bookmarkers. Those have no influence on your rankings. (very little value)
Last tip: don't worry about page rank.
I hope it helps. I probably forgot a few things but other people will add to my comment.
My post contains basic tips but it should give you a head start. I hope this is not a pelletage de nuage mais quelque chose d'interessant et qui pourra t'aider dans la construction de ton site.