@ib2 @T-3D I've been a domain investor for over 10 years and have been very successful at it. There's a lot more that goes into it then just registering a domain name and hoping it will sell. You can list your domains on Godaddy auction listings or on premium listings, I've had a lot of success with those. Some good resources are namebio.com, dnjournal.com, namepros.com and others.
If you are looking to sell a domain name that is no longer of use to you, a possibility would be to lease it through a third-party company such as Godaddy, which lists tens of thousands of names. If the name is a quality one, there are also premium agents such as MediaOptions, which deals with more selective domain names. An alternative option would be to lease it out on platforms such as Nameforest.com. Doing so will save you the time of having to find potential buyers, and will guarantee a higher success rate than attempting to look for a purchaser on your own.
If you are looking to monetize an idle domain, looking to third-party platforms would be a good idea. Many of these platforms such as Nameforest ourselves will create a logo alongside your domain, which will be added to the list of preexisting domains on their sites. This is useful as the demand for your domain will also be greatly increased after it is rented as opposed to a domain that leads to a blank site - thus making it easier for you to find a potential buyer.
If you buy keyword specific domains, you're really buying the type in traffic. I use the URL builder and redirect through that URL so you can see how much traffic your getting from the keyword domain. There seems to be no rythme or reason to what keyword domains deliver traffic and what don't. By tracking traffic with the Google URL builder you get a feel for what names are giving you traffic and which are not. ie. the plural, the singular, two words, three words, the possessive, etc.
So how do you develop that instinct? NameBio maintains a database of over 500,000 historical domain sales (as of writing this post). They have interesting filtering features by which you can narrow down domains by price range, date sold, keywords and more. Simply sifting through the listings on NameBio long enough will quickly develop your domain appraisal “instinct”.