Building backlinks is important

Building backlinks to increase your pagerank is very important. A backlink is actually when a site points back to your site. The more is the pr of the site that points to your site, the better are the chances of a search engine increasing your ranking. Take a note, the backlinks should only be from dofollow sites. The better is your ranking in search engines on your specific keywords, the more you can bank with adsense.
To make backlinks, search google for sites related to your niche and post a quality comment with your site link there(don't spam, leave a genuine comment).

Create atleast 4-5 quality backlinks for 2weeks, and see your ranking boosting.

Another way to find high pr blogs of your niche is by using a software called scrapebox, it can harvest urls related to your niche and can automatically post comments on them, but i say that just use it for harvesting urls and post comments manually so they don't get counted as spam.