1. In-depth articles

According to the MozCast Feature Graph, 6% of Google search results contain In-depth articles. While this doesn't seem like a huge numbers, the articles that qualify can see a significant increase in traffic. Anecdotally, we've heard reports of traffic increasing up to 10% after inclusion.
2. Improving user satisfaction

Can you improve your Google rankings by improving the onsite experience of your visitors?

In many ways the answer is "yes," and the experience of several SEOs hints that the effect may be larger than we realize.

We know that Google's Panda algorithm punishes "low-quality" websites. We also know that Google likely measures satisfaction as users click on search results.

"… Google could see how satisfied users were. … The best sign of their happiness was the "long click" – this occurred when someone went to a search result, ideally the top one, and did not return."
3. Rich snippets from structured data

Google constantly expands the types of rich snippets it shows in search results, including events, songs, videos and breadcrumbs.

The first time I heard about structured data was from a presentation by Matthew Brown at MozCon in 2011. Matthew now works at Moz, and I'm happy to glean from his expertise. His Schema 101 presentation below is well worth studying.
4. Video optimization

Pixel for pixel, video snippets capture more search real estate than any other type of rich snippet, even more than authorship photos. Studies show our eyes go straight to them.
5. Google authorship

Scoring the coveted author photo in Google search results doesn't guarantee more clicks, but getting the right photo can help your click-through rate in many results.

What makes a good author photo? While there are no rules, I've personally tested and studied hundreds of photos and found certain factors help:

Use a real face, not a company logo, cartoon or icon
High contrast colors. Because the photo is small, you want it to stand out with good separation between the background and foreground.
Audience targeted. For example, young Disney fans are probably less likely to click on an old guy in a suit who looks like a financial adviser.