Superb resource list Brankica, thank you. I've also included it this week's Erudition, not just because you're in a competition, but because it really is a resource we should all have bookmarked. Actually, I need to make it a study priority and see how many of the sources I can reasonably use on a regualr basis. Link to Erudition | Help files from Information Junkies Anonymous
If you publish whitepapers or offer downloadable PDF guides, for example, you should be tagging the embedded hyperlinks with UTM campaign parameters. You’d never even contemplate launching an email marketing campaign without campaign tracking (I hope), so why would you distribute any other kind of freebie without similarly tracking its success? In some ways this is even more important, since these kinds of downloadables often have a longevity not seen in a single email campaign. Here’s an example of a properly tagged URL which we would embed as a link:
Having large groups of content that all revolve around the same topic will build more relevance around keywords that you're trying to rank for within these topics, and it makes it much easier for Google to associate your content with specific topics. Not only that, but it makes it much easier to interlink between your content, pushing more internal links through your website.
The amount of dark social that comprises one's direct traffic is going to vary. For example, you might be diligent about incorporating tracking tokens into your email marketing campaigns, and asking your co-marketing partners to do the same when they promote your site content. Great. You won't have a huge chunk of traffic dumped into direct traffic that should really go into email campaigns. On the other hand, perhaps you're embroiled in a viral video firestorm, and a video on your site gets forwarded around to thousands of inboxes ... you don't exactly have control over that kind of exposure, and as a result you'll be seeing a lot of traffic without referral data in the URL that, consequently, gets bucketed under direct traffic. See what I mean? It depends.

Mobile traffic: In the Groupon experiment mentioned above, Groupon found that both browser and device matter in web analytics’ ability to track organic traffic. Although desktops using common browsers saw a smaller impact from the test (10-20 percent), mobile devices saw a 50 percent drop in direct traffic when the site was de-indexed. In short, as mobile users grow, we are likely to see direct traffic rise even more from organic search traffic.