All three sources are important but have varying levels of conversion, so you should calculate how much each traffic source is converting and deal with them individually.
The way a first-time visitor interacts with your site is very different from how a returning visitor interacts. To improve first-time visitors conversions you have to isolate it from the conversion rates of your loyal or returning customers and determine what they see when they visit the website for the first time and how you can improve that experience. Usability plays an important role in reducing the bounce rate for first timers.
There are two questions you should be asking yourself. 1) Why did the person return, and 2) did the person convert the first time around, and if they didn’t, why not and how can you convert them the second time around. Keep in mind, even if someone didn’t convert as a new visitor, you made enough of an impression to get them to come back. Now that they have liked you enough to return, your goal is to isolate the return visitor conversion rate and figure out how to increase that.
Even if your visitors don’t convert, it is important to monitor their behavior on the site. What exactly are they doing, how can you get them to do more of it, and how can you influence this behavior into conversions? For example, what are your page view rates per unique visitors, what is the time spent, comments or reviews made, and so on. Each of these interactions is important, and your goal should be not only to increase these interactions (e.g. increase time spent on the site), but also figure out how you can leverage these increased interactions into increased conversions (which might be downloads, subscriptions, purchases, etc.).
The value of a visit is tied directly to the interactions per visit. You can calculate this simply as number of visits divided by total value created. Calculating value per visit is difficult because there are many intangibles involved that create value that is hard to define. For example, blog visitors create value every time they add a page view to your traffic (because of cpm advertising) but they also create an intangible value when they comment on your site. Similarly, visitors on e-commerce sites create value every time they purchase a product, but they also create a somewhat incalculable value when they leave a product review or when they spread word of mouth.
The corollary to value per visit, and one of the most important metrics, is cost per conversion (alternatively: lead generation costs or cost per referral). It doesn’t matter if you have high conversions and high value per visit if your costs are so prohibitive that your net income is zero or even negative. While trying to increase conversion, keep your costs per conversion and overall margins in mind.
Your initial goal when trying to increase all five of the metrics above is to minimize your visitor bounce rate. The Bounce rate is the rate at which new visitors visit your site and immediately click away without doing anything (very low time spent and no interactions). A high bounce rate can mean several things, including weak or irrelevant sources of traffic and landing pages that aren’t optimized for conversion (have a poor design, low usability or high load times). Bounce rates for e-commerce sites are often called abandonment rates, i.e., the rate at which people abandon their shopping cart without making a purchase. This is usually a result of an overly complicated checkout process, expired deals, forced cart additions (e.g. to see the actual price of the product, add to your cart), and so on.
Your bounce rates aren’t entirely derived from your home page. In many cases your final call to action or conversion may be on page 2 or 3 of a process. To maximize conversions you need to dive deeper into your exits and figure out at what stage in the process your visitors are exiting the site or abandoning their shopping cart, and optimize the process accordingly.