Optimize it for humans, and it will be optimal for engines, too:

  1. Publish good material.
  2. Publish good material well! Standards for online content authors
  3. Link to good material.

OK, maybe that’s not the complete story but it’s the best you can get in a short answer. To quote Michael Torbert, maintainer of “All in One SEO Pack”, the most popular WordPress plugin currently:

The biggest thing, of course, for SEO […] is content. That will never change and it’s become increasingly, more and more important […] as the search engines get better and better determining what is on your page and parsing through all that data. So, having good content is the key.

Michael Torbert, AKA hallsofmontezuma, in: “All In One SEO To Go”

With that said, search engines can always use a little help to index a website better. There are two very popular WordPress plugins suited for this.

“Google (XML) Sitemaps Generator for WordPress” is a must-have. It automates the generation of an XML sitemap, a document recommended by the search companies themselves.

An XML sitemap tells web crawlers (also known as “spiders”, “robots” or just “bots”) where to find the content to be indexed. So, everything is indexed, even pages with no links, internal or external, pointing to them. An XML sitemap helps crawlers in other ways too. For instance, when a crawler sees the same content repeated in the home page and in the permalink of an individual post, it does not have to work too hard to decide which to give more weight to: it just looks at the XML sitemap, and learns that the main and permanent location is the permalink.

XML sitemaps and sitemap pages in websites are DIFFERENT things. The former are unstyled XML documents meant for web crawlers. The latter provide an index, an overview of the site’s content, for human visitors.

“All in One SEO Pack”, the other very popular SEO plugin, does various kinds of optimization. One is similar in purpose to XML sitemaps: It adds noindex tags (“do not index this”) to pages that duplicate content (category pages, tag pages, etc.), so that crawlers can work better.

It can also rewrite page titles, add meta descriptions, and more — see its page for details.

Both plugins work fine in their default settings. Just install and activate.