While search engine optimization can improve your rankings on Google, Microsoft and Yahoo, it is very hard to land on the front page of Google and Microsoft. So you have two options
You can spend your money and resources on optimizing your site so that you can get on the front page of Google, Yahoo or Microsoft. if you are a small to medium business, this can sometimes be impossible because of the way the algorithms work. So you can go with option two.
Instead of trying to get on the front page through organic keywords, you can buy keywords or bid in keywords so that when somebody searches for keywords that you are trying to target, your advertisement comes up on the sponsored listings on the page. This can sometimes be just as effective as appearing on the front page of Google, Yahoo or Microsoft. For every click that a visitor makes on the search engine to land on your site, you pay a small amount of money to the search engines. If done properly, and well tracked, you could achieve substantial conversion.