Most people believe that you simply need a name and a bit of time to make money when investing in domain names.
This is usually not the best way to make money.
What you should look for is to develop a few of your domains, the ones with a unique potential to prove that they are worth some money.
The added benefit is not only do you sell a domain with a genuine traffic, but you also sell lots of backlinks and already done SEO work. This can easily be worth a lot more than the domain itself and help you get a very nice return on your investment.