Have you ever had the sun glaring down from a clear sky with no natural shade in sight nearby? A photographer should always pay attention to the sun's position, but how best does one deal with harsh light?
If I am in an ideal location, the first thing I will consider is to block the sunlight in some way. Surrounding trees or nearby structures can come in handy. Again, if you pay attention to your subject's shadows, you can understand the position of the sun. In this way, you will be able to position them so that the sun is not casting shadows across their face.