what is the best way of link building....? If i do blog post .....how many blogs posting i should do...? they all will have 0 PR....should i post new article daily to particular blog site with some links..? Can i submit particular site page as a signature in forums..? This will once again have 0 PR.... Both options given above will work or not?
Comment on blogs. Participate in forums. Write very unique good content, and social bookmark it. Write very unique good content and submit it to article directories. Find articles in blog that are closely related to your subject that already have PR and that are DO follow, and join in, providing value to the discussion.
Post regularly so Google will crawl your blog frequently, do not do it to the point where you burn yourself out but just regularly, I'd say at least three timew per week.
Both options you mentioned will work when linkbuilding. Don't worry about PR as much, focus simply on getting the backlinks from good quality sites. Comment on blogs, post on forums, and keep posting on your blog.
I think that you shouldn't worry much about PR when link building. Arguably it is a plus to have links from websites with good PR but the only reason is that Google "seems" to like these websites since it has given them a good PR. I would try and do all of the methods mentioned above and my opinion is that submitting quality articles in article directories like ezinearticles or articlesbase is the best way to get links.