Let me add this one too here:
Matt Cutts (Google Engineer) confirmed that if you have less PageRank can also mean that a site wont rank well:
Quote:
ShyBoy, have you been collecting backlinks in any unusual ways? It
looks like you may have, and I would pay special attention to that.
For example, if you had been attempting to get PageRank via paid links
on various templates, then when that PageRank stops flowing (e.g. if
Google improves its detection in various ways),
the fact that you have
less PageRank can also mean that a site won't rank as well.
If that applies to you, my advice would be to pay special attention to
that issue, in addition to the other good advice you've already
gotten.
Matt
More:
Please Help! -60 penalty from Google due to proxy site. - Crawling, indexing, and ranking | Google Groups