There's a section in the guide called: Influence Your Site's Listing In Search. Note, this is more about how your listing apppears, rather than where it appears. It's more about improving clickability than rankings, although this stuff shouldn't hurt your rankings either.
Granted, there's not much in the way of new information, but it's nice to see what exactly Google is highlighting. The first thing under this section is a video from Matt Cutts (from 2007) about snippets:
It then lists the following as ways you can help create "compelling listings that users are more likely to click":
Create useful page titles. Make sure that your title is useful, descriptive, and relevant to the actual page itself.
Use informative URLs. The URL (web address) of a page appears below the title, with words from the user’s query in bold. Your URLs should be simple and human readable. Which do you find more informative: http://example.com/products/shoes/high_heels/pumps.html or http://example.com/product_id=123458?
Provide relevant page descriptions. The descriptive text under the URL is usually taken from the description meta tag on the page. Descriptions should be different and unique to each area of your site.
Add your business to Google Places, to help Google display location information in results.
Manage your sitelinks. Sitelinks (sub-links to individual pages on your site) are meant to help users navigate your site. Sitelinks are automatically generated. This means that you can't specify a sitelink, but you can use Webmaster Tools to ask Google to demote sitelinks you don't like.
With regards to sitelinks, Google actually made some adjustments to how they appear back in April. In Google's most recently monthly list of algorithm changes, there were four changes that had to do specifically with sitelinks. These were:
“Sub-sitelinks” in expanded sitelinks. [launch codename "thanksgiving"] This improvement digs deeper into megasitelinks by showing sub-sitelinks instead of the normal snippet.
Better ranking of expanded sitelinks. [project codename "Megasitelinks"] This change improves the ranking of megasitelinks by providing a minimum score for the sitelink based on a score for the same URL used in general ranking.
Sitelinks data refresh. [launch codename "Saralee-76"] Sitelinks (the links that appear beneath some search results and link deeper into the site) are generated in part by an offline process that analyzes site structure and other data to determine the most relevant links to show users. We’ve recently updated the data through our offline process. These updates happen frequently (on the order of weeks).
Less snippet duplication in expanded sitelinks. [project codename "Megasitelinks"] We’ve adopted a new technique to reduce duplication in the snippets of expanded sitelinks.
To demote a sitelink with Webmaster Tools, click "sitelinks" under "Site Configuration," add the URL in the "For this search result" box, and complete the URL of the one you want to demote in the "Demote this sitelink URL" box.