Search engines such as Google have hundreds if not thousands of ranking factors which they take into consideration to determine the ranking order of web pages and content in their search engines for any particular given term. The unique algorithms which each search engine uses to determine the ranking order is of course kept a secret to keep less than pure online marketers (see what is black hat SEO) from abusing those factors to game the system. That said, we can use a lot of intuitition and the occasional guidance from the search engines themselves (taken with a grain of salt, of course) to form ideas about what's important in getting our websites to rank atop Google and other search engines to garner them more traffic and ultimately more conversions on our ends.
What Are User Metrics?
User metrics are one of the most important ranking factors in Google because they literally and accurately convey to Google what people think of our content. Google cares about the opinions of its users above everything else, and how its users interact with your website falls under the umbrella of user metrics. This is a Google Analytics term which relates to how people interact with your site. Let's cover a few examples of user metrics and how you can improve upon each:
Time Spent on Site - The amount of time they spend on your site. Pretty straightforward, but the more time they spend on your site, the better that tells Google that your content is. You want to get this up as much as possible. I'll explain more on how to do this in the next example, which is bounce rate.
Bounce Rate - Bounce rate refers to the percentage of people who come to your website only to exit your site through the same page they came from. This could mean that they hit the back button on their browser, they closed their browser, typed another website into the browser's navigation bar, or they clicked on a hot link or search bar they have in their browser. However they did it, it means they presumably didn't like your content enough to stick around and visit additional pages. The more pages they visit on your site, the better metric that sends to Google. You have a content site worth exploring with content which is helpful and informative, moving people to look at more and more of it. It's a good idea to use a lot of internal links on every page of your site for this reason.
Pages Visited - This is another metric related to bounce rate, because the more pages which someone visits on your site (and in relation to bounce rate, more than one), the higher the quality of your content appears to be to search engines. Conversely, if someone exits your website after just one page, that says again that they didn't think much of what you had to offer, making it easy for search engines to knock you down in the rankings. Again, like I mentioned while discussing bounce rate, you can boost your pages visited stats by creating a lot of internal links to other relevant posts and information you've made on your site to keep people on your site.
Repeat Visits - Repeat visits are another indication that your content is of quality, quality enough to convince people to check back on your site later. This is in contrast to first time visitors. The goal is obviously to get your repeat visitors as close to the first time visitors metric as possible, indicating that near 100% of your unique traffic converts into returning visitors in the future. Create good content and maintain a consistent posting schedule when you upload new content and people will catch on that you're in this for the long haul and will continue to return to your site again and again.
Click Through Rate in SERPs - This comes into play for pages which are maybe at the bottom of the first page in the search engine results pages (SERPs) or somewhere on the second or third page of the SERPs. Search engines understand that these pages naturally aren't going to get as many click throughs because they're not as visible as the pages listed at the top of the SERPs. That being said, if you're getting more clicks than the search engines recognize as being average for that position or maybe you're even getting more click throughs than the pages above you, then that will tell the search engines that they've got their ordering wrong and they'll give you a nice boost which will in turn give you even more clicks and traffic. The key here is to create a good headline which makes people have to, not just want to, click through to your page. See this article on how to increase your click through rate in the SERPs for more information.
Traffic - This is a bit of a chicken and egg scenario, where search engines will reward you with better rankings if you have a lot of traffic, but how can you get traffic without good rankings? This is where the other metrics and elements of SEO and other sources of traffic can help you. Nice.