One of the most fascinating benefits of online business is its ability to track many types of user behaviour. One of the best examples (and one of the most important ones) is the “dark social” category of Website traffic source.
As Tom Tunguz notes, “dark social is a massive and to date little understood force despite its importance. Dark social clicks originate from instant messages, emails containing links and links embedded in tweets opened in TweetDeck among other sources. Google Analytics buckets dark social as direct navigation, incorrectly assuming these users spontaneously typed a long url from some epiphany.” A huge list of possible sources is here.
He also shows a way how to track the traffic using Advanced Segment. The point is to create a new segment that excludes the landing page that exactly matches “/” and the Source contains (direct).
However, the best method is to use common sense. If you find (direct) traffic and look at the landing pages, you may find pages that have very long URL. It is very unlikely that your user remembered such a long URL and manually typed it. The example of such a link is xxx.blogspot.com/online-marketing/4483/this-is-the-url-i-am-talking-about-and-it-still-does-not-end-only-now.
Some marketers have tried to develop a code to overcome this obstacle.
Finally, as the best practice, this is another example of why it is necessary to tag your campaigns, so that you try to lower the amount of (direct) traffic as much as possible.