Start by reviewing googles webmaster guidelines and see if anything you are doing is listed there as a nono... They look at your outbound and inbound links. How many are there? How fast did you build them? Are they to/from bad things - porn warez, gamling, etc. Mike
no luck much. some reasons are getting backlinks from high pageranked sites quickly or getting your links on link farms
A website that I know got penalized by Google, because the ex of the owner worked at Google. A manual penalty for around 2 months! That's what you get for cheating! Maybe you did something simular