can any tell me about all the basic factor on which google penelise a site?? and types of penalisation
Keyword Stuffing is one of them. If you have too many keywords on a page, google will actually put you in a lower ranking.
hey ! Quality content will never let you penalize in SE. even if you have done the keyword stuffing at a limit, the quality content that has been updated on regular basis and contains quality text in it, could save you penalties.
Posting in a couple 0PR directories will not get you punished. Excessive posting in directories might get you punished tho, according to google any directory is not good, especially if you pay for inclusion to a high PR directory. It is very rare that a site will get banned by google, but excessive link exchange with irrelevant site is one reason that can get you banned. Excessive anything can get you punished, you have to make your linking campaign look natural.
If you over optimize the website. Keyword stuffing is bad. If you have a new website and you get fake backlinks surge that ends quickly.
Excessive link churn - this is where an unnatural number of links appear / disappear. This filter is ignored if your content based on a trending news topic. Perfect anchor text profile - 100% identical backlinks could be risky. But then again, there is a theory that Google can't penalise based on factors outside of the site owners control. Meaning a competitor could decide to blast your site with 1 million crappy links to do you over. So the theory is that the big G will just ignore instead of penalise. But in practice I have seen a number of penalties applied to sites ranging from -10 to disappearing from the index altogether!