When aiming for the perfect shot, remember to keep sunlight in mind. Too little and you can't see the subject. Too much and one of two things happen. The first is that too much sunlight is directed into the camera's lens or on the subject and washes out the picture. The second is the person being photographed has to blink or close his eyes because of the massive amounts of sunlight coming into his eyes.
When composing your picture, pay attention to the weather. If it is overcast outside, try to keep the sky out of your picture as much as possible. Black and white pictures are also a good choice if you want to shoot outside on an overcast day. If the weather is nice and sunny, you will get a lot of great pictures, just make sure your subject isn't squinting at the sun.
Make sure the background you choose complements the subject of the photo. If you take a photo of a model against a busy background, the viewer's attention is going to be drawn to the background rather than the clothes. As a general rule, simple backgrounds with colors that contrast with those of the subject are ideal.