In this thread on DNForum.com titled "Domainers start with mistakes?" a forum member asks if he was the only one who registered rubbish domains when he started buying domain names or if others have made the same mistakes when having been new to the glittering business of investing in domains.
I can tell you this, everybody makes mistakes. No matter how long you've been to the game, you will always do something wrong, be it buying above value or selling too cheaply. I don't want to sound like a know-it-all, but I've made countless mistakes myself, so take it from someone who has quite some experience in getting things wrong.
The first domain name I bought with the intent to resell at a profit was totally worthless! Its actual value has been negative in many ways: I wasted both money and time registering it. I had made the mistake of believing an automatic domain appraisal tool I had found somewhere on the Internet. The tool wanted to convince me that the domain in question was worth some $10,000+. Of course, I believed it, hurried over to my registrar and bought the domain. It has been such a bad name that I don't even want to post it here. It would be too embarrassing, as I've said on DNF already.
Really, don't let such things bring you down. Especially when being new to this, like in any other business, you'll go through a learning process and you will do the one or other mistake along the way. Just make sure to not lose too much money in the process.
I wrote a popular article about getting started as a domain investor in late 2007. I'm going to update that article some time in the future, but most points still hold true today. For example, if you're new to domaining, it might be a good idea to set yourself a monthly budget that you can afford to lose. This way you won't lose too much money if your investments don't pan out as planned.
Every time you make a mistake, that's a lesson you learn and the next time you'll do better. Reading and learning from others is very important, too, but learning by doing is what lets you gain valuable hands-on experience.
Listen to the domain veterans, participate in discussions on domain forums and don't be afraid to ask questions. Most people I was lucky enough to get to know in the domain industry have been very helpful and willing to share their knowledge. Also, don't forget to subscribe to the various domain blogs that have come up over the past 24 months. You can find my favorites on my blog's right sidebar. They're true treasure chests full of domaining wisdom. Enjoy!