What is the easy way to build one-way link?

with higher pr and do follow - do it. all are one way link exchange
post blog comment with higher pr and do follow blogs,
post forum posting with higher pr and do follow,
article submission, directory submission, social bookmarking, press release, search engine submission .........

 

There is no easy way to get backlinks (you want quality, not quantity although of course the more the better). It's best to combine all sorts of methods: forum and blog posts, directories (especially niche, smaller ones), article writing, social bookmarking. But mostly keep adding quality content to the website. Google will love it and you will attract natural linking this way.