"PR" like in page-rank, NOT SERPs (search engine ranking position) for a google search ? PR you get by building links and promoting, URLs in sigs, link exchange, link building. SERPs you get with good SEO of your site for keywords.
Yes, valuable backlinks and quality content of your website could help. Also, you can write valuable articles with your keywords n the signature link. But why you need a higher PR and which is the one you have now?
1. Submit to directories like DMOZ. 2. Do some article marketing. 3. Link exchanges with other sites using networks like http://www.3waylinkz.com/