Here you need to invest. Domain names are valuable internet real estate and some people actually make a nice living off of buying and selling them. One strategy is to use Google Adwords to find keywords that are trending and use that information to buy domain names that you think may soon be in demand. However, since short, snappy, or straightforward domain names have already been mostly snatched up, you can also get lucky buying domain names that are random acronyms, as you never know when a person or company with those exact initials will decide to set up a website. (CPC.com, for example, sold for over $200,000 when Contract Pharmaceutical Corporation decided to go online). The biger domain name company is www.goDaddy.com , register here and you can start searching a good domain name right now and buy it. After that you can sell it in www.sedo.com, www.afternic.com and www.aftermarket.com or in godaddy auctions.
Selling your domain in sedo and afternic you have to use expanded promotion options when possible, it is a way to expose your domains to more people depending on where you have them registered. With Afternic, the Premium Promotion level exposes your domains 75 million searches each month compared with 25 M at the network promotion level. Just making this small change will triple the chances that someone will see your domains and make an offer.Also you have to properly categorize your domains. Many people search for domains, but other many like to browse and look through a particular category when they don't have a specific domain in mind. If your domain is not categorized correctly they may never see it.
You can try sell your domains directly searching companies who may be interested. Search in Google the keyword of your domain and contact to the webmasters, they may buy if your domain name is better or if they want to avoid a new competitor. Other group ot interested people is whoever owns the other extensions of your domain.
Mainly .com is very popular domain extension and you can sell .com domain name easily. Each year tens of millions of dollars are exchanged during the resale of domains. Recently Quinstreet the domain name insure.com for $16 millions.