Wot? Ermahgerd... Link building isn't necessary any-more. All you need is social sharing buttons on your content, if your content is good, then people will share it.
You must get backlink from high PR related sites. Its boost your sites PR. So, make more backlink in high PR site as you can.
Within 3 week I have archive page rank 1 of of my website and for the inner page 3 page rank. I have submitted in all high page rank.