The right lighting can make or break a photo. If you have a digital camera, get familiar with your camera. It might include some settings that could come in handy such as a "cloudy" setting, an "indoor" and "outdoor" setting. It you have a digital SLR always check your iso settings as well as your white balence settings. This will make a difference with the type of tones you will get in a photo.

A general rule is to get your subject out of the sun. They will feel alot more comfortable and no one looks good with squinty eyes. Lighting is usually best in the morning around of before 10 a.m. or in the early evening.

Check out this article by Jim Story which explains how to use a flash to fill in lighting when taking a portrait.

dog

This is a photo I took Spring 2007 around 8 a.m. at a 5K. I chose my subject matter and waited till he was in front of the sun. I knelt down and was able to get a nice rim light around him.

london

This photo was taking as the sun was going down, a perfect example of a nice time to take a breathtaking photo. The sun created a pretty sillohuette of the Tower of London against the amber-colored sky.