To summarize for the original poster:
Outdoor portraiture can be challenging, since you have to work with
what nature gives you. There's a lot to consider, but here are a
few basics:
Direct noonday sun tends to be harsh and unflattering. Early
morning and late evening light is generally better. It's softer,
and comes from the side, which better illuminates and models facial
features.
Overcast days can be great, particularly when the light has a
"pearly" quality to it. On these days you might need to take steps
to ADD contrast, however.
If you are going to shoot when the sun is high in the sky, you
should do one of several things:
Shoot under some sort of cover so that your light comes from the
sides, and preferably from just one side. Shooting under cover
gives more diffuse light. Letting light in from only one side
provides some shadows and modeling to your subject.
Shoot with a diffusing panel between the sun and your model to
soften the light and stop it down some. Then use reflectors to
light the shadows. This requires stands, or better yet, assistants
holding your diffusers and reflectors.
Use fill-flash, set a couple of stops lower than your sunlight, and
preferably diffused. You want to brigthen the shadows, but don't
want to create a second set of shadows, which looks unnatural.
With outdoor lighting just like studio lighting, you need to
consider your lighting type (spot or diffuse) and direction, and
make sure your lighting ratio (highlight to shadow) doesn't exceed
what your medium can record, unless you're after a high contrast
effect. You can use reflectors or fill flash to brighten your
shadows.
People tend to squint when they are in direct sunlight, or looking
at something very bright, which is unflattering.
You also want to watch out for bright and distracting elements in
your background. You have to be very consious of what appears in
the frame, and weather it helps or hurts your compisition.
--
http://www.pbase.com/duncanc