See the form it takes. This is not easy. When you get a vague image, go with it. Let the shapes change as your vision focuses. Open your eyes again and get a new form to help the vision continue to grow.
Shapes can change and the vision can move.
Just let the flames shape the images they will. After you have your visions, thank the now departed fire, open the circle, and try to make sense of what you have seen. Think about what you saw and ask what it means to you. With practice, anyone can see the visions in the flames. Just as anyone with a book can do a tarot reading, it takes skill and work to figure out what it means.