Finding the perfect domain name is extremely important. This has proven itself over and over again. The domain name has to be something unique, easy to remember (so it has to be readable and preferably short) and don’t forget, easy to write. Also it has to represent you, your business/product or your brand.
But that is all for the human user. What about the search engines?
Domains with words separated by -s (hyphens) are considered separate words by the search engines, but beware: too many and it’s more likely to be considered a spam domain than an actual domain. Keep the number of hyphens to a maximum of 3.
Furthermore, if you provide a service mainly in 1 country or a specific region (like the European Union) use the according TLD.
Since Google became an official domain registrar in early 2005, the age of the domain counted as well. Since a domain that has been existing for several years is more likely to be an authoritative source of the information it provides than a domain that just started. Also, spammers are known to frequently change domain names to avoid being blocked by spam filters and alike.
A final good tip I recently read, try to register your domain per 2 or more years. This also gives more credibility to the domain name.