Understanding light direction
When the main light comes from near the camera position, shadows tend to fall behind the subject. Detail can be clear, but shape and texture may look flatter.
Side light
Light from the side creates visible highlights and shadows across the subject, which can reveal texture and three-dimensional shape. Move yourself or the subject and watch how quickly the balance changes.
Backlight
With the light behind the subject, edges can glow and backgrounds can become bright. Exposure can be trickier because the camera sees a large bright area. Check the subject rather than assuming the meter has made the decision you want.
There is no best direction
The useful direction depends on the subject and the photograph you are trying to make. Learn to recognise the direction first, then decide whether to move, wait or modify the light.