Google, being the largest and most used search engine and is extremely important to optimize your website for. As a matter of fact, if you optimize your website just for Google youd find your rankings in Yahoo! and MSN will jump up higher than your ranking in Google. Ive optimized many websites that show up in at least the top 20 listings in Google and found that in each case they ranked higher in Yahoo! and MSN usually in the top 3 positions with most in the number one spots.
Most everyone agrees that with Google content is king. So writing good copy with just the right amount of keyword phrases, for keyword density is important. And natural anchor text links is second to the throne, which takes lots of work and proper timing to do properly.
Third in line are keyword phrases (notice I said phrase because single keywords are almost impossible to optimize for), which need to be researched to find the right phrase for you and not used to often in the content/text to get the right density. Used to often and youll hurt your ranking.
Fourth in line are the Meta Description Tag which when used properly can actually bring visitors to your website who wouldnt...