Today Google has announced Google’s SEO Starter Guide that says

We thought it’d be useful to create a compact guide that lists some best practices that teams within Google and external webmasters alike can follow that could improve their sites’ crawlability and indexing.

There are also “pitfalls to avoid” that are listed here:

Page title tags:

• choosing a title that has no relation to the content on the page
• using default or vague titles like “Untitled” or “New Page 1″
• using a single title tag across all of your site’s pages or a large group of pages
• using extremely lengthy titles that are unhelpful to users
• stuffing unneeded keywords in your title tags

Description meta tags

• writing a description meta tag that has no relation to the content on the page
• using generic descriptions like “This is a webpage” or “Page about baseball cards”
• filling the description with only keywords
• copy and pasting the entire content of the document into the description meta tag
• using a single description meta tag across all of your site’s pages or a large group of pages

URL structure

• using lengthy URLs with unnecessary parameters and session IDs
• choosing generic page names like “page1.html”
• using excessive keywords like “baseball-cards-baseball-cards-baseballcards.htm”
• having deep nesting of subdirectories like “…/dir1/dir2/dir3/dir4/dir5/dir6/page.html”
• using directory names that have no relation to the content in them
• having pages from subdomains and the root directory (e.g. “domain.com/page.htm” and sub.domain.com/page.htm”) access the same content
• mixing www. and non-www. versions of URLs in your internal linking structure
• using odd capitalization of URLs (many users expect lower-case URLs and remember them better)

Navigation

• creating complex webs of navigation links, e.g. linking every page on your site to every other page
• going overboard with slicing and dicing your content (it takes twenty clicks to get to deep content)
• having a navigation based entirely on drop-down menus, images, or animations (many, but not all, search engines can discover such links on a site, but if a user can reach all pages on a site via normal text links, this will improve the accessibility of your site

HTML Sitemap

• letting your HTML sitemap page become out of date with broken links
• creating an HTML sitemap that simply lists pages without organizing them, for example by subject

404 page

• allowing your 404 pages to be indexed in search engines (make sure that your webserver is configured to give a 404 HTTP status code when non-existent pages are requested)
• providing only a vague message like “Not found”, “404″, or no 404 page at all
• using a design for your 404 pages that isn’t consistent with the rest of your site

Content

• writing sloppy text with many spelling and grammatical mistakes
• embedding text in images for textual content (users may want to copy and paste the text and search engines can’t read it)
• dumping large amounts of text on varying topics onto a page without paragraph, subheading, or layout separation
• rehashing (or even copying) existing content that will bring little extra value to users
• having duplicate or near-duplicate versions of your content across your site
• inserting numerous unnecessary keywords aimed at search engines but are annoying or nonsensical to users
• having blocks of text like “frequent misspellings used to reach this page” that add little value for users
• deceptively hiding text from users, but displaying it to search engines

Anchor text

• writing generic anchor text like “page”, “article”, or “click here”
• using text that is off-topic or has no relation to the content of the page linked to
• using the page’s URL as the anchor text in most cases (although there are certainly legitimate uses of this, such as promoting or referencing a new website’s address)
• writing long anchor text, such as a lengthy sentence or short paragraph of text
• using CSS or text styling that make links look just like regular text
• using excessively keyword-filled or lengthy anchor text just for search engines
• creating unnecessary links that don’t help with the user’s navigation of the site

Heading tags

• placing text in heading tags that wouldn’t be helpful in defining the structure of the page
• using heading tags where other tags like <em> and <strong> may be more appropriate
• erratically moving from one heading tag size to another
• excessively using heading tags throughout the page
• putting all of the page’s text into a heading tag
• using heading tags only for styling text and not presenting structure

Images

• using generic filenames like “image1.jpg”, “pic.gif”, “1.jpg” when possible (some sites with thousands of images might consider automating the naming of images)
• writing extremely lengthy filenames
• stuffing keywords into alt text or copying and pasting entire sentences
• writing excessively long alt text that would be considered spammy
• using only image links for your site’s navigation

Robots.txt

• allowing search result-like pages to be crawled (users dislike leaving one search result page and landing on another search result page that doesn’t add significant value for them)
• allowing a large number of auto-generated pages with the same or only slightly different content to be crawled: “Should these 100,000 near-duplicate pages really be in a search engine’s index?”
• allowing URLs created as a result of proxy services to be crawled

Social media promotion

• attempting to promote each new, small piece of content you create; go for big, interesting items
• involving your site in schemes where your content is artificially promoted to the top of these services

General promotion

• spamming link requests out to all sites related to your topic area
• purchasing links from another site with the aim of getting PageRank instead of traffic

Fairly standard stuff from the big G, nonetheless worth a look.