Regarding analytics, be sure to also consider event and goal-driven analytics, and funnel analysis. You can do this in Google Analytics by firing events, setting events as goals, and using virtual pageviews as event funnel steps. You can also use the free tier of Mixpanel for this.

So, for example, source A might send you twice the traffic of source B, but source B gives you three times as many newsletter signups, blog comments, or pageviews.

Also, your goal might be for people to register on your blog and comment. You may get lots of traffic, but few comments, and not know why. When you set up a funnel such as View Page=>Register=>Confirm Registration=>View Comment Form=>Submit Comment, you might notice that people are dropping off at a specific step in the funnel. Maybe they're not getting the registration confirmation email, or something like that. A properly-configured funnel will show you where the dropoff is. You can also segment that funnel, to see, for example, if maybe people using Chrome are getting through the funnel at twice the rate that people using Firefox. Maybe in that situation you have a browser display incompatibility. Or the funnel is dropping off at the registration confirmation step; maybe in that situation your registration confirmation emails aren't getting delivered. Etc.