Most important tags for optimization

Title:

<title>your phrase</title>
the most important tag for most of the search engines
(if you use it correctly).

1) use only simple phrases.
2) don't repeat words more than twice.
3) the targeted keyword goes first.
4) use more than 30, but less than 80 characters.
5) don't use words that are not in the page content.
6) every page should have a different title.

Alt:

alt="image description"
very important tag for search engines and especially for blind people who are surfing the internet with voice browser.

Headings:

<h1>headline</h1>
<h2>headline</h2>
<h3>headline</h3>

Very important tag.
Having a <h1>Headline</h1> on each page that is the same as the page title could improve things slightly.

Meta tags:

Don't be brainwashed by all the huge quantity of articles about Meta tags. Meta tags are almost useless nowadays. It may help a little if you use the description tag.

Description Meta tag:

 The only tag still being recognized by search engines today (2004).
<meta name="description" content="description of your site or page">

Key word Meta tag:

Some very old search engines also recognize the keyword Meta tag, so I still use it.
<meta name="keywords" content=" Webmaster, designer, programmer, ">

You can delete all the other meta tags as they are useless nowadays.

Useless meta tags:

<META content=all=index,follow name=robots>
<META content="15 days"name=revisit-after>
<META content="local, global" name=distribution>
<META content="Pump Design software" name=description> <META content="tlb, default" name="Microsoft Border"> <META content="MSHTML 6.00.2600.0" name=GENERATOR> <meta name="ProgId" content="FrontPage.Editor.Document"> <!-- keywords: keyword,keyword,keyword -->
<meta NAME="SUBJECT" CONTENT="import adviser"> <meta NAME="RATING" CONTENT="GENERAL">
<meta name="GENERATOR" content="Microsoft FrontPage6.0">
<meta name="ProgId"content="FrontPage.Editor.Document"> <meta NAME="REVISIT-AFTER"CONTENT="10 DAYS"> <meta NAME="LANGUAGE" CONTENT="EN">
<meta NAME="COPYRIGHT" CONTENT="MiroWeb.com"> <meta NAME="ROBOTS" CONTENT="All">
<meta name="Accessibility" content="This site is compatibile with,Netscape 4.7 and above, Internet explorer 4.0 and above on Mac and PC, Also IBM Screenreader 2" />
<meta NAME="bla bla bla" CONTENT="bla bla bla">

Don't delete this one:
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252"> This tag is for foreign users so the text will show up correctly on a different language browser. (New browsers don't need this one either.)
 

http://www.gorank.com/analyze.php - Professional Keyword Density Analyzer

http://www.1-hit.com/all-in-one/tool.search-engine-viewer.htm - The search engine spider simulator checks if your site can be spidered by search engines. It will give you an idea how search engine see your page