When it comes to SEO plugins, Yoast's WordPress SEO plugin has become the go to for most webmasters. While there are several SEO plugins that may be slightly easier to work with or have slightly different features, the Yoast SEO plugin for WordPress is the most complete SEO module ever created. It is very well documented and supported by most theme authors. Installation takes minutes, and there are several extensions, like SEO Extended and Yoast Local SEO, which improve upon it's already robust feature list.
Our general process with Yoast on every website is pretty similar. We install the plugin, configure the social options and hook up our Webmaster/Analytics accounts, and begin to optimize our pages. If we have an existing website with dozens of pages and posts, we generally will install the extension SEO Extended. This plugin adds a feature to Yoast that allows you to set all of your Page Titles and Page Descriptions from one page, without having to open and edit every page/post individually. There are literally thousands of articles covering best practices with page title and descriptions, so we won't spend time covering that in this article. Look for a tutorial in the coming weeks that covers a wide variety of best SEO practices.
Once you have your titles and descriptions set up, pull up the source code for a random page or post on your site. Check to make sure that the Page Title makes sense. On a lot of installations your WordPress generated page title and Yoast page title will run together. If this is the case you need to set the plugin to 'Force Rewrite Titles'. We generally tick this box, just to be sure.
In addition to adding your social profiles, Google accounts, and page title and descriptions, the Yoast plugin allows you to set taxonomies and default meta values for your different post types, and also has a feature that will clean up theof your website. There are a lot of SEO Experts that will argue that search engines prefer a clean head. For a more thorough explanation of what each feature of the plugin is and what the best practice for each option is, head over the Yoast's Definitive Guide to WordPress SEO.