To get free traffic from search engines like yahoo or Google you need to create great content.

A great content is what is genuinely created to benefit your visitor.

As people find your pages and discover the valued information, they will:-

1. Refer your site to their friends
2. other publishers will link to your site for key information regarding the subject matter to their own site visitors.

when these two things happen, you begin to build the "off-site" momentum which the search engines will reward you for.

But I must let you know that this takes time.
so...
to avoid spending weeks, months building later to find out that it is not working, you need to do the following

1. Build your own niche ( everybody is good at something. find out what you are good at that will be of benefit to someone else when you share it).

2. Based on what you decide, research what people are searching for that relates to the topic.

3. Then build your website/blog around it.

There are tools to use and a step-by-step information on how to make this whole thing simple and easy to follow.

I hope this helps