The way is, finding and leave a comment in a dofollow blog. It works! Just try it.
But, what is dofollow blog?
Dofollow blog is blog that delete 'rel=nofollow' in comment-section. It means, if we leave some comments in their blog, Google will crawl it as a backlink to our blog. Mostly, blogger is still let their blog in 'nofollow'. So if we leave any comments in their blog, Google will not follow or ignore it and for the impact, we do not have a backlink from comments in their blog. Isn't it a pity?
So.. it's time for hunting 'dofollow' blog?!!! :D