Card games are probably a great place to start learning game mechanics and layout because it's a standard rule set, you have a set number of cards with their own image an value - so handling them neatly is quite easy once you have, say 52 plain objects textured with the card faces. You might end up rewriting stuff a lot until you get a good system, but having a solid base like a deck of cards to work from is the best way to learn.
Starting with just a system that lets you shuffle and distribute the cards into hands etc would be a good start, a lot of people prefer to get the basic game system in place, using text for example. I'm not saying that's wrong, but when you have a system like DBPro it's so quick to get media in place and looking good that it can really fuel your motivation. A text based Blackjack game is something that would teach you a lot, but having something your proud to show other people from early on makes you want to finish it, and that's where the buzz comes from that keeps us going.
The most successful projects here tend to be the ones that take a simple game mechanic, and present it well. Starting with a card game will teach you enough to move onto other projects like puzzle games, board games, types of arcade games too. Casual gaming is really our forte at the end of the day, more people should be realistic and capitalize on that.
