Given that you can register domain names for as cheap as $6.95 per year, it makes sense to register your top keyword phrases, and then use domain pointers (also known as domain aliases or domain forwarding) to redirect visitors from your “pointer” domains to your main domain.
For example, if your main website is at www.houseplans.com, you may want to register the following domains: www.houseplan.com, www.house-plans.com, www.unique-house-plans.com, and www.homeplans.com, and set it up to have each one of these forward visitors to your main website. This can make sense to capture visitors who may type in variations of your main domain and singular vs. plural forms.
Another technique is the use of subdomains, also known as prefix domains or third- level domains. For example – http://keyword.domain.com.
Google currently treats a subdomain as an entirely different domain name. Each subdomain is redirected to a different folder on your website – for example, www.keyword.mydomain.com could point to www.my-main-domain.com/keyword/. This is an excellent strategy is your site is comprised of related but distinct groups of topics.
Contact your webmaster or web hosting provider for specific details on how to set this up as it varies from one server platform to the next. There is usually a small fee associated with setting up pointer domains and subdomains.