First, clean up the avocado. Wash it clean as a bean. To tell which end is the pit goes in the water, it's the wider end. Carefully stick four or five toothpicks evenly spaced around the middle of the avocado pit and rest the toothpicks on the edge of the glass.
Place the glass on a sunny windowsill. Check on it daily. Refill the glass so that one third to one-half of the pit is in water all the time. Your patience will pay off when the roots begin to grow, followed by the stem and leaves (two to eight weeks).
You may want to start a few avocados in case one of your pits is a dud. A fizz-out. When the plant is about 12 inches high, transfer it to potting soil in an eight-inch pot and cut one-half inch off the stem to encourage more fullness.