How Drupal can help with SEO and meet Google's guidelines
Create unique, accurate page titles
This should be one of the most important parts of your SEO campaign. As with a lot of SEO work, picking good titles mostly comes down to picking the right keywords to target and creatively using them. Drupal helps by making content easy to enter through simple forms. Changing titles and other content is a no brainer with Drupal.
Make use of the "description" meta tag
This tag is printed at the top of your web pages and provides a brief description of the page. Google and other search engines often use this as the descriptive text block under the link to your site in search results. Some SEOs say that this text isn't too important, and that it doesn't affect how you're ranked. But Google advises you to use it and it is one of the first things a searcher sees.
So how can Drupal help? The Meta Tags module provides you with an easy-to-use box on just about every page you edit. One installed, no special knowledge is required to enter the description data and you can focus on writing good content!
Improve the structure of your URLs
The ways in which Drupal helps out here are a bit technical. Basically you don't want your URLs to have a bunch of numbers and random characters in them. You want them to be human readable and structured logically.
Here's a link from RideBuzz showing how this can be accomplished with Drupal's Views Module: http://ridebuzz.org/city-rides/us/MA/Amherst. The URL pretty much tells you exactly what you're looking for. In this example 'us', 'MA', and 'Amherst' are all 'arguments' to a Views page and tells it which data to display. More importantly, in terms of SEO, it is a very clear way to tell search engines what the page is about.
Drupal also comes with Path, which allows you to change the URL for regular pages, or "nodes", (otherwise they'd come out node/1, node/2 etc).
Pathauto makes this part easy once it's installed and set up. It automatically takes the title you enter for a post and formats it into a new, human-readable URL. Global Redirect makes sure all the original node/1 type URLs get sent over to the nice URLs pathauto creates for you.
Good practices for site navigation
Use breadcrumb navigation
These are links at the top of the page showing you where you are on the site. For instance, if you're looking at a Macbook Pro, the breadcrumb might be “Home >> Store >> Products >> Laptops >> Macbook Pro.” Drupal makes this easy: it's standard with every Drupal installation.
Put an HTML sitemap on your site, and use an XML sitemap
The Site map module helps make putting together a site map a snap and it won't include any broken links.
XML Sitemap will create an automatically updated XML site map for you. Once the module is set up and the site map is submitted to Google and other search engines, you're good to go.
Have a useful 404 page
The 404 page is what a visitor will see when they visit a page that doesn't exist. Showing them a useful message will help them get on track navigating your site.
Standard Drupal provides some decent options for customizing your 404 pages and the CustomError module is definitely worth a look when you need more configurability.
The Search 404 module is cool. It gives the visitor search results based on the URL they entered, which doesn't exist. This is especially good if the URL they're trying to visit has been changed and the content exists elsewhere on the site.
Part of being optimized is making sure that when somebody finds a 404 through a search engine, they can still get to where they want to go.
Be aware of rel=”nofollow” for links
Setting links to 'nofollow' tells search engines that your site does not want to 'vouch' for the site being linked to. This is especially useful when you allow visitors to comment. If they add spam links to your posts, your 'nofollow' tag, when added to their link, will tell google that you're not willing to put your reputation on the line.
Drupal comes standard with a robust input format system which specifies which users can enter in which HTML tags, if any. It also offers a “Spam link deterrent” option which adds 'rel=nofollow' to links.
While these are great tools, be careful to not overuse 'noindex, nofollow' and block too much of your own content from search engines.
Make effective use of robots.txt
Drupal comes default with a good robots.txt file, which bars search engines from indexing administration and a number of other pages.
Drupal's defaults are usually pretty good here, and it helps by keeping pages out of search engine results that would only confuse the user (typically because they would get "Access Denied" if they tried to click on them).
Take advantage of web analytics services
Web analytics services tell you who's coming to your site, from which regions and sources, how long they're staying and more. Google Analytics is a great free service and setting is up on Drupal is made easier with the Google Analytics module.Get Clicky is also popular and there's a Drupal module to help set that up too.