Get high PR back links. However, PR is little use if anyone else also gets the same PR score. So, focus on quality contents on your site.
I agree with lightless's advice of following Google Webmaster guidelines: http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=35769
IP does matter. If financially possible, do get a dedicated IP and web hosting for your site.
Google posts penalty on sites that point to bad neighbourhoods or sell ads without nofollow. Did it happend to your site?
I agree PR is updating. Is there tools that can tell you the real time value of PR, not Goolge toolbar PR?
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