Agree with the comments above you can either have many low pr or few high pr backlinks or you can have a mix of both... choice is yours
Just Two things: Getting links from Related high PR sites Posting unique and quality content regularly
agree with them..more quality backlinks is the key...but don't focus that much..focus more on SERP ranking and traffic
why you targeting PR, you can target SERP, if you want PR, you can try back links from high pr sites.