How would you define a successful fiction writer?
Different kinds of success. You succeed if you manage to entertain. If you can show people something important. If you can make them think. If you can have them keep looking out for your work because it connects with them. If you can take the complexities of the world and give them a ‘flesh and blood’ relevance through the fiction. It helps too if you can also make a lot of money from it. Awards are irrelevant.
If you are addressing a group of aspiring writers now, what is the one vital message you would convey to them?
Stand up and live before you sit down to write (Thoreau, I think). Then write honestly in a voice that is yours. Write regularly. Make time for it. Read a lot (no limits). Think a lot. Dream a lot. Then just have the guts to do it, never mind what anybody else says about you, your writing, or your dream of being a writer. And remember that in the act of writing, you are a writer and no one can take that away from you.