Well, what is the product or service you'll be offering? Can you find a domain that corresponds to it? If not, can you come up with something that is available, and is easy to say and spell? The shorter the better - always. Also, .com names are always the best choice (when choosing a TLD).
depends on what you need the domain for. its always a good idea to get a domain name with your desired keyword in it if possible.
the name should be short and easily to remember. also is should be everyday word that people use so that they dont have to remember the name.