From the Drupal module page, "The Metatag module allows you to automatically provide structured metadata, aka "meta tags", about a website."

Download over 3.5 million times, this module is an insane query builder. Learn it.

Create XML Sitemaps and automatically send them to search engines when content is updated or added.

Amazing module that integrates with both the db and solr (it also supports other backends but some contrib modules don't.)

Redirect users to different URIs

Takes care of many small SEO related tasks related to URIs.

One of the main features:"Once enabled, an alias provides a nice clean URL for a path on a site. However Drupal does not remove the old path (eg node/1234). The problem is that you now have two URLs representing the same content. This is dangerous territory for duplicate pages which can get you

"The Pathauto module automatically generates URL/path aliases for various kinds of content (nodes, taxonomy terms, users) without requiring the user to manually specify the path alias. This allows you to have URL aliases like /category/my-node-title instead of /node/123. The aliases are based upon a "pattern" system that uses tokens which the administrator can change."

Gives replacement tokens. This module is used by so many other modules, you are sure to use it and learn it if you haven't already.