Basic link building is easy. There are some well known, although not particularly effective tactics that almost everyone does now. Getting content written and posting them on article sites is one. Guest posting is another, although Google has said that it is the same thing as paying for a link and has reduced the efficacy of it. Forums posts are nearly useless now but is something that you will still see on popular forums even with nofollow. To get the most out of your link building efforts, that is to get links that actually pass authority, takes some work, here are some ways to go about doing it:
One of the best ways to get good quality links is to make amazing infographics that will spread through sites like Pinterest and Facebook. When bloggers post them, you will invariably get some good and often related backlinks. Good infographics require a lot of prep work, research and are costly to design. Because of that cost in time and money, it still has not been abused as a technique.
Edu and Gov links
The .edu and .gov domains still carry a ton of link juice. This is because unlike any other domain it is extremely hard to get backlinks from any of these sites. We are talking about government agencies and educational institutes like universities. Getting these links will cost money as you will have to either sponsor an event or forum organized by such a place. The good news is that these links will be on the sites for a very long time.