So just what is a "premium" domain?
Unfortunately, it may just be the one you want. As with any other market driven product or service, supply & demand plays a role in the value of a domain. With over 7 billion people in the world and only so many possible word & word combinations available, there is a great demand for the better domain names.
As an example, the more costly Real Estate tends to be the beachfront property, often in a warm climate where you can take advantage of the climate and make the most use of it. With domains, marketers want the best possible keyword or keyword combinations to boost their search rankings, as well as having a name that is easy to remember, to keep customers coming back, or to use in their advertising.
Also important is the extension. Even after the dot com bubble in the early 2000's, the one thing people remembered was just that: .com. And therefore it is still the most popular extension. Many people don't even consider anything other than .com for a commercial website. The three most popular extensions today remain as .com, .net, and .org. In certain countries, country code domains are also very popular, but often have a limited audience, such as .de (Germany), .fr (France), etc. In the United States, .us has been available since 1985, and can be a less expensive alternative to .com or .net, or where the other major extensions are already in use. Note that many country code extensions (including .us), have specific requirements about who can own them. For .us ownership requirments, please see the nexus information here: http://www.neustar.us/the-ustld-nexus-requirements/
Many people also consider a domain's age to be an important factor in determining value. And while this may be partially true, it's not the age in itself that makes it more valuable. The simple fact is that if it was first registered when all the "beachfront property" of domains were registered, and has not expired, chances are better that someone placed value on it long enough to keep paying the renewal fees over the years.
Also be wary of "domain backorders". Many registrars offer services that attempt to get a domain for you when it expires, and while this may work for a few obscure domains, most people are not going to let their domains expire, especially if it is generating income for them, or has value to them in some other way, such as their personal name, their blog, or has their business website on it.