The conversion rate is an incredibly powerful metric, it measures what happens once people are at your website and it can show you, if you're running a strong advertising campaign that makes a lot of people interested in your product or not!
What is "Conversion Rate"?
Definition: The conversion rate is the percentage of users who take a desired action. The archetypical example of conversion rate is the percentage of website visitors who buy something on the site. – Nielsen source
Conversion Rate = Number of Sales / Number of Visits
Example: An ecommerce site is visited by 100,000 people during one month, and 2,000 users purchased. Thus, the site's conversion rate is 2,000/100,000 = 2%.
It's not just about the conversion rate
An higher conversion rate doesn't always mean an higher perfomance: an increase in conversion rate can be caused by a vast decrease in visitors coupled with a more gentle decrease in sales, too! So, let me explain well what does it means and what are some other aspects you need to focus on.
You shouldn't maximize the conversion rate, you should optimize it. The difference is that sometimes it costs so much to increase conversions that it's not worth doing. It's more profitable optimize first it.
Breakdown your data using conversion rate in a right way
Create a breakdown by channel: separate out your channels, figure out which you can impact through conversion optimization, and focus on those instead of your headline conversion rate.
Create a breakdown by visitor type: try to split out "new visitors" vs "returning visitors" on different dimensions.
Create a breakdown by device type & location: split out your different visitors on mobile, desktop and tablet and cities, ordering it by conversion rate.
You would find useful a dashboard I created in Google Data Studio which you can download it for free, by clicking this link and adding your Google Analytics' data.