First of all concentrate on your each and every page of contents. It should look good and not copied from somewhere. and it should be related to the public interest. After this do directory submission which has high pr. Each and every directory will give u link on his site.
1. Blog commenting on high PR do follow blogs 2. Be a member of high PR forum (like DP) 3. List your website on directory lists 4. link trades, 5. Article marketing etc, you can do lot of ways
Blogs and forums are probably the easiest ways to generate links, use the link in your signature with your anchor text. Article marketing is also good, sites like Ezine have high PR. These are some of the easiest methods but they are very effective.
Yes, only find high PR blog to comment and do an honest coment not just a spam one then you will get a nice feedback.
I would say it is very hard to get high PR backlink with free method However, if your site has very rich and great content, then people might give you backlink And yes, blog commenting is one of the method but as known that all those high PR blog is mostly owned by seo personal, and most of them are using "nofollow" tag to prevent from spammer