Casting a circle
First, cleanse the area using burning sage or your broom, then take your athame, or your index finger of your power hand and, starting at the north, visualize a pure white light streaming from it to the ground... walk slowly in a clockwise direction, visualizing the light forming a wall around yourself and your altar (if you have one). While doing this I say "Here is the boundary of the sacred circle, let naught but love enter in, let naught but love emerge from within." I then walk the boundary sprinkling salt and repeating the phrase above, followed by incense, the south candle and then sprinkling water as well. If you are outdoors, you can plunge yor athame into the ground and say "as above, so below", sealing the circle into a sort of sphere that completely surrounds you and the area within, or, if you don't have an athame or are working indoors, pat the ground in the north direction three times and say "As above, so below". Your circle is cast and now you can call the quarters.
How to close the circle: Starting again at the north, take your athame or index finger and move in a clockwise motion, visualizing the pure white light of your circle being drawn into the blade or your finger. I usually say "The circle is open yet unbroken" while doing this. Finish in the north and either ground the energy by dispersing it into the earth or save it in your athame for use at a later time. Always thank the quarters before you close the circle, as well as any deities or other beings you've invited in your working.