I agree that this is definitely not a quick answer. As Ozkary mentioned, sharing/starting great content topics on social networks is a GREAT way to get some qualified traffic, but remember that most social networks obey the "no-follow" tag. For those who don't know what the no-follow tag is, it's an attribute that goes in the code of the link that tells Google to not pass any "Link Juice" through. Remember that every link to your site is essentially a vote of confidence to the search engines, hence why link building is so important. Enough jargon...I'll try to answer your question without going into too much technical detail.

There are TONS of ways to build links. However, there are typically 5 main types of links that I show my clients how to build. Over the past couple of years, I've developed an efficient way to find these kinds of sites to build links. Oh, and by the way...these links happen to NOT use the no-follow feature and have high Page Rank. I provide the sites, my clients build the actual links. Without further ado, here are the 5 main types of link building:

1. Forum profiles - Create profiles on certain forums and strategically include your link
2. Blog comments - Tailor your message to the topic of the post and respond with an anchored link in the name section (must be rather careful with this method)
3. Directory submission - Just like it sounds, finding the right directories that will actually help and not penalize you...that's right...some directories can actually hurt your link profile
4. Social bookmarking - You can leverage these types of links with RSS pingers to not only get your site indexed quicker, but drive some targeted traffic to your site
5. Article submission - In my career, I have found these types of links to be the strongest types of links that are in your control. Writing great articles around your keywords will yield some very valuable authority

I hope you gained something out of this! Email me at RankingChannel@gmail.comn if you have any further questions my friend.