Photographers rarely shoot in the mid-day sun because the sunlight is direct and very harsh, this harsh light, casts very hard shadows. The midday sun comes from too high an angle, to produce a flattering portrait. It causes subjects to squint, and their eyes become lost in deep pockets of shadow.
Try and shoot early morning or late afternoon for your best results. The light is warmer and softer just after sunrise and just before sunset -- the pros refer this time as 'The Golden Hour'.
If you must shoot a portrait outdoors at high noon, try and find some shaded areas, a trees canopy is nature's perfect umbrella. Have your subject stand in the tree's cover, you get some really nice soft light, and produces a very flattering portrait.