For this trick to work easily, it's best to have an analog watch. (The kind with the minute and hour hands) If you have a digital watch, draw a watch face on the ground showing the current time.
If your in the northern hemisphere what you do is point the hour hand on your watch towards the sun. From there simply bisect the angle of the hour hand pointing towards the sun and the 12 with an imaginary line. The imaginary line points south.
|With this information you now also know which way the other directions are.|
If your in the southern hemisphere, point the 12 toward the sun and bisect the angle between the 12 and the hour hand with an imaginary line. This line points north.