When lighting a portrait remember to keep it simple. Consider the use of one light and modifier at first. This is considered your main light and set the power according to your preference and vision. Take a few test shots to determine if the light matches your vision and adjust accordingly. The use of the histogram on camera may be of use to determine proper exposure. Since this image was shot outdoors, Instead of adjusting the power of the flash I simply moved it away from the subject. A second light can then be added to “fill” the shadows. This light is usually set to lower power than your main light. More lights can be added but I rarely find it necessary to use more than two or three lights and a reflector at most for portraits.
In the example below the image was shot outdoors with camera and flash’s in manual mode for total control over the lighting.The main light set to 100% power. The second light used as a fill only set to 20% and distance of flash to subject both adjusted. Both lights were used with white umbrella modifiers for a softer light. Although umbrellas tend to “spill” light and not my first choice for indoor or studio lighting they tend to work fine for outdoor use since “spilling” of light isn’t as much of a concern outdoors. For indoor use I do prefer using light boxes with grids for more control of the direction of the lights and therefor less spilling.
In Post production the image was converted to black and white to place more emphasis on the subject and avoid distraction of the background.