Drupal naturally does well in search engine rankings. There are a few things that you can do to help improve those rankings like using
Pathauto,
XMLSitemap, and
Meta Tags. I've written a little bit about Pathauto and XMLSitemap and now--Meta Tags.
Metatags are less important than they used to be in SEO. They are subject to abuse with most search engines relying on keywords on a page rather than relying on meta-data to determine what a page is all about. That said, adding meta-data to your site can't hurt your rankings and can help.
The Meta Tags module allows you to easily meta tags to your pages potentially improving your search engine rankings.
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Actually, meta tags are more important than many people realize, at least the 3 main ones that have been the traditional focus of SEO.
The first one is not really a meta tag at all, but is often called one because it is commonly found in the source code hanging out with them. This is the TITLE <.title> tag. This is crucial for your pages to be optimized. It should be less than 70 characters, contain as many keywords for the page as possible, but still be a good English sentence that describes what the page is about.
The second one is the DESCRIPTION tag, it should be under 250 characters and this give you a chance to use many your main keywords for the page to describe what the page is about. Here too you need to use proper English so the text is not only found in the seach engines, but also provides what the user is searching for.
The third one is the KEYWORDS tag and this really is not very important, but improper use can hurt a page in my experience. This too should be about 250 characters with the keywords and keyword phrases separated with commas. The keywords should be different for each page depanding on the page content. I have seen it hurt pages where they all have the same thing in the keywords tag. So better to leave it empty "" then all the same thing.
FYI - Meta-tags are also still a requirement to meet full Accessibility. You need the big three Title, Description and Key Words along with the language tag at the minimum.