But in general, the best and easy way to sell a domain is to go with a marketplace. There is many popular marketplace dedicated to selling domains including Flippa and SellDom to sell your domain (full disclosure, I’m working on SellDom). The advantage is to leverage the popularity of that kinds of services in hope that someone will find your domain and buy/make an offer.
If you are feeling ambitious, you can link each of your domain names to its matching “buy it now” purchase page at one of the marketplaces. Another more sophisticated option would be to “park” your domain with one of the leading domain parking companies, such as DomainSponsor or SmartName and enable their built-in “for sale” message and contact mechanisms.
Unfortunately, most domain names take at least a couple of months to sell, especially without an attached website. Thus, there is no need to become discouraged if your domain name does not sell immediately. Most people make the mistake of quitting their domain speculation endeavor after waiting for several months to sell without success. In reality, domain name squatting can be just as profitable, and it is a valid form of long term investing.

I did this last month, snagged a great domain that no one else found and got it for $69 because I waited until the last moment to place my pre-bid. Flipped it within a week for a little over $1,000. And probably could have gotten more if I sat back and waited 6-12 months, but a bird in the hand… (plus I like to keep turning over inventory and maintaining cash flow).

Those trading domains for commercial purposes are generally on the prowl for lucrative domain endings. There are essentially two different ways traders go about making money off of domain names. One method entails purchasing already established names for a low price and selling them for a profit later once their value has increased. Another strategy involves buying and registering a domain that is thought to possess a high sales potential. Many domain traders use backorder services. These services automatically register a domain when one becomes available or is deleted (what are known as expired domains).
It's ranking high today! What could be the problem? NO. JUST STOP. Unless you know the entire history of a domain, you may be setting yourself up for failure before you begin. SEOs (and business owners) use a variety of tactics to get a site ranking high in search results. For some of these methods, we'll just call them "questionable". These methods could include everything from buying links, overuse of directory submissions (non-industry related), duplicate listings, poor quality backlinks, and guest blog comments.
It is much harder to sell names no one has heard of. Short names have the highest value — they are rare, easy to sell and bring substantial profit. Basic and common domain names, which can be relatable, or arouse interest in the market are the best. General names sell thick and fast and also bring considerably higher profit.  Names that are easy to spell will attract buyers, and provide good opportunity to make a decent profit. If you know you have a good domain in your hands, then you are likely to make good profit by selling it.
Using the keyword search feature you’d also be able to familiarize yourself with how much domains typically cost on average in a certain industry or niche. Even better, they have an addictive little app called “The Domain Game” available for iOS and Android. They basically give you a domain and you try to guess whether it sold for three, four, five or six figures. You get points for each correct answer and lose points for incorrect ones. You do this for a while and you start to see patterns. Your brain starts connecting the dots and you get better it. Now you’re ready to go out there and scout some domains!