The best place to start would be on something flat like a bed side. My truck was owned previously by a landscaper (yuppie name for gardener) and he carried a bunch of rocks in it. There were quite a few good dents. Using a hammer and dolly can be rewarding but you have to go slowly and lightly when doing it. If you are too hard you can stretch the metal. Try just to "massage" it with the hammer and take your time.
Doing a hubcap is possible but you might want to try a sandbag for a dolly especially if they are chrome.
A recent issue of Hot Rod magazine had an article on hammer and dolly work.
