The easiest and least time consuming option is to 301 redirect the old domain to your existing site. This tactic obviously works best if both sites are in the same sector and are targeting the same keywords; otherwise, if you have a pet supply site and you buy an old Texas Hold 'Em poker site, a redirect probably might raise some eyebrows among the search engines. If, however, your site is and you buy and 301 redirect the domain over, you're inheriting a lot of topical and appropriate links.
The biggest advantage of using expired domain names to earn cash online is that they belonged to a website that had already establish, registered with several search engines companies and has existing backlinks and traffic. In general, by making use of expired domain names you tap into the resources that were created by someone else to get rich within a short time unlike when you do all the dirty work to get your website recognized immediately.
By strategically buying expired domain names which have certain quality features, you can create a link "pump" to your target sites. From an SEO perspective, this can turbo charge your rankings on Google and other search engines. Also, you can make money directly by promoting products on high ranking search results. Additionally, you can make money by selling links on your network to people looking to get an SEO boost.
Thousands of domain names expire every day. The reasons are different. Some owners forgot to renew the domains, some just don't want them anymore or they moved on to other projects. For most people these so called Expired Domains don't have any value. They just see a bunch of Domain Names someone else deleted and move on, but for the people who know about SEO or the value of good Backlinks, Expired Domain Names are money just waiting to get picked up from the street. The only problem is to separate the good ones from the bad ones. That is where comes into play.