Most web analytics programs track hundreds of variables. To come up with a predefined list of metrics that are the same for all webmasters equally would be a daunting undertaking, if not impossible. What works for your website may not work for others. You may not get a lot of traffic to your website but the people that visit tend to buy from you. But there are a few metrics that most webmasters feel the need to track. They are also the metrics that tend to be common across most web analytic software packages.

Bounce Rate
Bounce rate is the number of single page visits divided by the total number of entrances to that page. Typically, a high bounce rate indicates that visitors were not interested in what the page had to offer or convey. However, this is not always the case. Suppose you gave your readers exactly what they were searching for and the page answered the question they had. They no longer need an answer so they leave your page. In other words, you gave them too much information. If you instead, gave them some of the information and then you asked them to subscribe to your newsletter in order to get the rest, this will not only help your bounce rate but it will build your list as well.

Exit Rate
This is the last page that a user visited on your website. It’s the place where the user decided that your website is no longer relevant to what they are seeking. If you see a page with a high exit rate, you may want to try and determine what it is about the page that is making visitors leave. Perhaps there is no call to action. It could even be something as simple as grammar errors. Paragraphs that are too long and wordy can also generate high exit rates.

Average Time Spent on Page
If Google sees that you have pages that people are spending a lot of time on, they are going to reward you with higher rankings, all things being equal. If this number is high, you are likely doing something right with respect to the content you are presenting. Try to determine what it is about the page that is keeping people on it and do more of the same.
As stated in the first paragraph, there are many other metrics that you can track and what I believe are the top three may be quite different than what others believe should be the top three. Over time, you will develop your own priority on which metrics to track.