PR Juice can be called as importance which passes through one web page to another from links. For getting more and more PR juice you must use do follow directories for all off page activities because Do follow = Share PR juice + back links.
Formula is very simple. Try to get one-way link from relevant sites having Good PR with less outbound links.
I have heard of using what is called a link wheel, the way it works is you build a page on sites like squidoo, hubpages or blogger all with a link back to your site and then link them together squidoo to hubpage hubpage to blogger blogger to squidoo, there can be more spokes on the wheel but you get what I'm saying. Then you write mass articles linking to your spokes and then spin and submit.
Good ranking still requires backlinks from other domains with good authority and ranking. Setting up weak sites to feed link juice is not very effective.