When creating fun, natural, lifestyle portraits, there's really nothing more beautiful than natural light. However there are several things to remember when you go out to photograph.
1. Place your model in the shade to avoid direct sunlight. If you can, scout out the place where you're going to be photographing. Look for natural reflectors such as a sidewalk, patches of clay or stone, dirt or sand and have your subject stand in the shade but at the edge where the natural reflector will cast light on your subject. Your model will be comfortable, her eyes won't be squinting from the sunlight, and you'll have nice even light with no harsh shadows.
2. Always focus on the eyes. In portraiture the eyes are the most important aspect and the most expressive! It's the first thing we look at. It doesn't matter, in fact it's usually more flattering, if everything else is a bit out of focus.
3. Shoot with a wide aperture for a shallow depth of field. This will make for a smooth and more flattering portrait. With a shallow depth of focus your model will pop out from the background.
4. Speaking of backgrounds...Be aware of the surrounding scene. Make sure there's no competing elements such as power lines, signage, or distracting objects that might distract the viewer. It could be as simple as taking a few steps one way or the other so as not to include the distraction in the frame.
5. Lastly and most importantly... Have Fun! No matter where you're photographing if you're not having fun and engaging your model then your photos will lack that genuine beauty that's unique to you and your model!