The right domain name will help people remember your website address, making it more likely that they'll visit your site and tell their friends about it.
Also, if you include keywords (the words people use in search engines to search for your site) it can help increase your ranking on search engines.
Domains that end in .COM are the standard and most memorable. Even if you want a local URL, like .US, you may want to get the .COM version as well, and forward all traffic to your extra domains to the one domain that's attached to your website.
- Use your brand/business name in your domain
- Don't use an acronym that is difficult remember
- Try to include keywords
- A .COM domain is typically preferable
- Check for double meanings brought on by lack of spacing
A great domain name would be www.OceanRoseWhaleWatching.com. Not as memorable would be www.orww.biz.
We recommend reading SEOmoz's excellent guide to choosing the right domain name.