From the horses mouth

Official Google Blog: Introduction to Google Ranking
There are a lot of words being written around how to achieve good Google results. I think that sometimes you need to go directly to the horses mouth and see what they say. This link is to the Official Google blog and is the first part of a discussion around ranking and is a reminder how you can be penalized for doing the wrong thing.
However, the thought crosses my mind that it is almost always better to just do the right thing and you will have a website that your customers will enjoy and link to as thus rank well. Probably, the only losers are possibly people that use a lot of graphics on their site.
To find out what Google sees on your site you can't beat the Google Webmasters tools website. This if nothing else will show you Google is not perfect (Some of my back links keep appearing and disappearing).