Light is your best friend and worst nightmare.

• Best light is dawn followed shortly by dusk as the angled direction of sun's rays causes long shadows making the shot more real
  
• Worst is noon as shadows are very short and right below generally not even being captured by the camera
• Also, at noon, shadows are harsh and one side of the face will be too dark. Shadow of nose will throw strange dark patch on one cheek
• Also, noon as highest contract (diff. between brightest and lightest in an image) and you want a good contract not high and not low
  
• At noon, take shots in the shade. See White Balance for more on this.
• If you want to be creative then bad weather is your best bet.

Colors of light
One easy way to master light is just to set your camera's white balance properly. See White Balance for more but understand the colors of light below.

Morning light is warm
Dusk is warmer
Sunlight is warmest
Cloudy sky is cool
Shade is cooler
Indoor light is coolest

For best results you want your images, specially portraits to have a "warm" color.

Artificial Light
Bounced light is best
Light coming from behind the camera but from around 4pm or 8pm is very good
Light coming from 11am or 1pm from behind the subject can create amazing halos