Michael,
I suggest you start reading here on Namepros. Also start reading on Domaining.com. You need to carefully study the domains that sell every day. Study the extensions, the words, the prices, etc. You need to know a deal when you see one.
Otherwise, buy low, sell high, like any other investment. Learn how to research a domain name on your own. It's history, value, potential end users, etc.
Domain names are a very complex area of investing. We are all teaching you. "We" means every domain investor that has ever posted here on Namepros, and every person that contributes to the industry.
Take your time. Set short term learning goals for yourself. Always search for your answers before asking questions. You will learn much, much more that way.