1. Reflect your branding. This is critical and often gets ignored.
2. Be short (but not too short – What is c.com?)
3. Memorable (i.e. a word or company name)
4. Have a common TLD as uncommon TLDs violate #3
5. A keyword or noun doesn’t hurt if your branding isn’t important.
Targeted keyword as part of domain name is pretty important, but not too important. It should be relatively short, memorable, marketable etc.