Ways to learn to season food correctly?
My best recommendation is to taste as you go.  Taste the initial product...raw vegetable, ingredient from the can, bottle, etc. and then continue to taste and sample a dish throughout the cooking process to see how flavors develop/diminish and enhance one another through the cooking process.

Learning to season food is a process of educating your palate and developing a "flavor memory"

One of the most important factors is to use enough salt.  Food that is properly seasoned with salt shouldn't taste salty but will have a brighter more vibrant flavor of the ingredients that are in the dish.  Food must be cooked with salt for this to occur.  Food that is seasoned at the table will merely taste salty as the salt doesn't have a chance to dissolve and pull the juices out and help them mingle with one another as happens during cooking.

The more of the basic flavor profiles that you can incorporate the more lively and flavorful anything will be.  Even before cooking you can take a look at a recipe and "disect" its flavor profile by determining which ingredients will add sweetness, sourness, etc.  If you notice that it's heavy in one direction or another, the flavor profile of the item(s) missing will likely improve the dish.  Then it's a matter of deciding what ingredient with that flavor profile would be best to add to that particular dish.

Shameless (but applicable to the question) plug:
If you're ever in Savannah, GA I offer a class called "Flavor Dynamics".  It is focused entirely around understanding how flavor develops, what affects our perception of flavor, and how to create well rounded flavor in your food.