1 Domain Company: Purchase domain from a credible company. Otherwise, in future you will be in trouble.
2 Short domain: Try to get maximum short, meaningful and relevant to your business. But dont go for short meaningless combinations.
3 Keyword and Domain: Find out best keyword relevant to your business try to include that in your domain name.
4 Try to get a unique one. Dont imitate any other famous website.
5 Try to avoid numbers and hyphens in domain name.
6 If .com availabe, dont go for another one. first book that one