Practice using the Exposure Compensation dial on your camera.
Having a big open space behind you, as opposed to trees or dark buildings, will help keep your subject’s face bright even when they have their backs to the sun. The best combination is to find a location where the sun can be behind or at an angle to your subject while placing them against a dark background – like the very trees you’re trying to avoid having behind you.
Put the open sky as much behind you as possible with the sun (and a separating, dark background) behind your subject. This minimized shadows on the girl’s face and the sun provided a pleasing rim light around her hair and shoulders. When shooting on Program, Aperture Priority, or Shutter Priority modes, you can override your camera’s exposure quickly with the Exposure Compensation dial.
In short, a great formula for outdoor, high-noon portraits without additional tools is to have open sky behind you and the sun’s direction behind your subject, preferably filtered through darker scenery. Want to improve this even more? Put a reflector in front of your subject. The sun coming from behind them will hit that reflector and bounce that light back into the front of your scene.