I agree with Bob - purchasing and tasting tobaccos in the same general category or family is probably the best way to learn the subtleties within a given group. I started with various aromatics, and quickly moved on to Latakia blends, then added in Va/Per blends, and finally some codger Burleys. I'm saving straight Virginias for later. :D
Your sense of taste is like any other sense - you can train it over time to pick out subtle differences that are not immediately obvious the first time. To use a culinary analogy, it's like the difference between white pepper and black pepper and cayenne pepper. Most people can tell the difference between cayenne and black pepper in a dish, but the difference between white and black is a little more subtle. Once you've tried them all, you learn to distinguish the smaller differences.
Your sense of taste is like any other sense - you can train it over time to pick out subtle differences that are not immediately obvious the first time. To use a culinary analogy, it's like the difference between white pepper and black pepper and cayenne pepper. Most people can tell the difference between cayenne and black pepper in a dish, but the difference between white and black is a little more subtle. Once you've tried them all, you learn to distinguish the smaller differences.