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.
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.
Keep an eye on the weather outside. Weather conditions can create many opportunities to improve or destroy a great picture. You can still get some great outdoor shots on a cloudy day. Compose your photos so that the gray sky is not actually in the frame. Don't let it stop you from taking great pictures.