Starting on domain names could be just a hobby or a pass-time endeveour of yours. How about making some money on your investment? Normally you would have few domain names for your own use, whether you write blog posts, your journal or technical/medical/science/travel stuff you are interested in is of no consequence. You have steady influss of readers finding your articles entertaining or informational and you get nice comments and some bad ones.
You are game. Really. All you need to do now is to have your domain name start earning your money.
There are many ways you can acheive that. The most common and amongst the easiest and less time consuming is to put your domain name in the Google Adsense program. This way you will earn some spare change and your time you could still invest in that what you like.
Second way would be to find some affiliates for the topic you are writing about. This is a bit harder and more time consuming to do but the end effect is much greater than the first method. Usually you would hunt for your competitors (even blog writers have competitors) and see what do they use and how. Once researched, you would go and check each of those affiliates your competitors use and see which one fare good. Also you would need to see if there are bad apples by doing online research on them. I know this sounds a bit too much when starting but end results are much worth the hassle. In average by affiliate marketing and good read blog or news site you can earn ten fold the amount your would using Google Adsense.
And finally there is a big jump. Being ready to sell a product or service. This is the hardest thing to do since you need to research the market, other competitors, get approvance if necessary, incorporate yourself if necessary and the whole deal can take months to set up and you would need to invest pretty much everything at the beginning and that with no ROI on sight for a year or two. However, if you really want to make real money this is the way you do it.
A few words if you do not write articles or you do not plan to have your journal/news or similar site. So you are in just for the money. In this case you are really only limited by the money you have to invest. You can set up parking page for quick turnaround (use Sedo.com for example). You can invest in hosting, host the sites and use article writing services to get some content to them then finally go the Google Adsense path – takes more time but it also takes much more ROI than simple parking domain names. And of course you can invest even more time and pay for good design, pay for content and introduce affiliate marketing. This will bring the major ROI, but you would have to balance your time between buying prospecting domains, selling the ones you find poor in name or potential and doing the maintenance on your existing sites.