Many Pagans and Wiccans celebrate and practice within a Sacred Circle. Prior to our rituals, we mark off, cleanse, and dedicate our Sacred Space. Where you point your finger, wand, or Athame (or sword, or staff...) to cast your circle will depend totally on the area you are working in and the number of people included in the circle.
Generally speaking, you should make sure that your circle is large enough to accommodate what you will do. A circle for a single person sitting in meditation will be far smaller than a circle for a dozen dancers around a fire. And a circle doesn't have to be perfectly symmetrical when cast, either. You can swerve to go around trees or rough terrain, for instance. Once the circle is completed, a sphere is formed, creating sacred space.
One method of casting the circle is to create an "energy ball" between the palms at heart level, then channel energy into this sphere until it is large enough to contain your ritual. It's a very natural form of circle casting, and I encourage you to experiment with this style. It's perfect for casting a circle when alone, or in a public place.
~Flame RavenHawk