Search Engine Optimization (SEO) is some kind of mystery. Because the big search engines don't reveal their complete methods of spidering and ranking it is always some guesswork to determine what's right and what's not. In general SEO boils down to tuning three things: content, meta headers and URLs. This document should give you some ideas how DokuWiki works in these areas and what additional SEO methods are available.
DokuWiki tries to produce semantically correct and valid XHTML. This means the structure of a document is easy to analyze by an automatic spider.
However how good the produced HTML is is highly dependent on a pages source. You should try to markup your document in a logical way. For example use headlines in descending order beginning with a level 1 headline. Use headlines for headers (not a bold paragraph), use lists for things that are a list and so forth.
DokuWiki creates all relevant headers to identify the page content (doctype, encoding, language).
The keywords or description meta headers can be adjusted through meta or tag plugin. However the popular search engines do not use these headers anymore because of extensive abuse by spammers:
You're right in that we generally ignore the contents of the “keywords” meta tag. As with other possible meta tags, feel free to place it on your pages if you can use it for other purposes - it won't count against you.
Google Webmaster Central
DokuWiki tries to fight wiki spam by several ways. One of them is called delayed indexing and directly influences how search engines spider your page. When enabled it will set the robots meta header accordingly to the age of a page. Only pages which were not edited for a certain time (default: 5 days) will be allowed for spidering. The idea is that the community will have removed any spam in this time. This means only a page which is considered as good by the wiki users will be added by search engines. If you have a quick community (eg. at this wiki spam usually never lasts longer than a day) or have a closed user group you may want to lower the indexdelay option or even set it to 0 for disabling delayed indexing.
By default DokuWiki uses the pagename in the title element. You may want to use the first level 1 header instead by enabling the useheading option.
DokuWiki normally uses URLs in the form of http://example.com/doku.php?id=page. Many search engines recognize this as a dynamic URL and change their spidering behaviour 1) accordingly. Google does spider such URLs but recommends to keep the numbers of used parameters low.
To improve the readability and help other search engines with your wiki, DokuWiki comes with a config option for two different methods of URL rewriting to produce nice URLs.
Adding the useslash option helps to increase your ranking further.
When a page does not exist, DokuWiki will issue a 200 OK HTTP response. In a wiki this is a wanted behaviour. However, it is speculated that search engines may perceive it as indicative of a link farm. You can enable send404 to make DokuWiki respond with 404 Not Found to requests for non-existing pages.
Several big search engine providers like Google, Yahoo and Microsoft allow you to submit whole site structures to their search engines through the XML Sitemap service. DokuWiki can automatically create an XML sitemap containing all of your wiki pages. See sitemap for more info.
On some PHP installations the PHP Session ID is appended to each URL of your wiki. This is not desirable in terms of SEO. Please refer to the rewrite page for a solution.