I agree with Rand about 90% of the time and he can make better videos than I can. Rand's first rule, "make the name brand-able" is the guiding principle, however several other factors are important. Also it is not easy to pick a good "brand-able" name with a .com that is not already taken. So you must invest time and effort to achieve the desired results. You may also want to consider buying a premium domain. For example I purchased the domain name OnlinePasswordManager.com (OPM) for $300, which is a super bargain. I would be willing to sell the OnlinePasswordManager domain name for $400,000 if anyone is interested.
Business.com sold for $7,500,000, and I know a guy that bought HalloweenCostumes.com in the early days of the Internet for $20, and he sold it for $820,000, an excellent return on his investment.