Casting a circle is not necessary with this ritual.Here are the preparations needed for the ritual of Dragon Fire:
If you have been given a Dragon's name and want to call upon him / her specifically use this name instead of the word "Draconis" at the End of the call in the Dragon Fire ritual. Visualize Dragon power and fire streaming from the Dragon Pentacle and entering the candle. After several moments, light the candle and for the fullest benefits the candle should be allowed to burn completely out after the ritual is ended.