I am going to explain to you one of the absolute easiest ways to get traffic from search engines today. It´s really easy, and it can be very effective. But it doesn´t have to be very effective, this is just if you do things right.
I will be brief. If you buy expired domains, you might get traffic from visitors searching for content that was on the old domain. It takes time for the “history” of the old site/domain to be deleted from the search engines. They have already been indexed, and if you buy a good expired domain, and you redirect this domain to your site, you might get nice value for your money.
An expired domain, is actually a domain that the previous owner didn´t renew (for some reason).
You can read the experiences of an Internet Marketer that tried this technique.