How Does Your Garden Grow?

This being the third year in our house, I am thinking that I should really get this whole gardening thing under control. Does anyone have any pointers for me? Last year my mother in law and I purchased flowers from the local conservatory and all of mine died, I mean, DEAD! Hers were gorgeous so obviously we were not sold bad flowers (the thought did cross my mind, although I am not sure that is possible). I am thinking of planting tomatoes, berries, and tons of flowers but don't know where to start. So if you have a favorite flower, type of tomato, or piece of gardening advice, please post!