There are MANY ways of casting a circle. Some branches of Paganism or Wicca have their own rituals. Depending of what path you follow, if you follow a particular branch you might want to do a circle ritual corresponding to that path. If you are eclectic or follow your own path, then pick a ritual that best. In general, there is no official way of casting a circle since Wicca has NO official doctrine.
There are many rituals that have to do will circle casting:
Find a ritual that best suits your own belief!