When assessing the lighting for a shot, always consider what your ambient light is doing. In this case I had to use the sun as my primary light and two flashes as my fill light. I under-exposed my shot by two thirds of a stop to get a beautiful dramatic sky. Mother nature was particularly generous because we had a westerly wind blowing and it gave the models hair and dress some movement. I love this effect.
You will notice that although her hair was moving there is no motion blur on the image. This is because I used a "fast" shutter speed to under-expose my ambient light without going beyond the constraints of my camera's sync speed (1/200th of a second). You will also notice that my ISO is low (64). I did this to further under-expose the ambient light to emphasize the blue sky.
There are a number of advantages that you gain when using the lowest ISO that your camera can offer. You get the least amount of digital noise, which equates to clean, clear, detailed images. The dynamic range is superb on most modern sensors at low ISO settings. You have much more control over your exposure. When you don't have the luxury of High Speed Sync and you want a relatively shallow depth of field without using neutral density filters, the extended low ISO settings can allow you to drop the exposure a bit further.
I didn't use a light meter in this shot, so I had to take a test shot and use my intuition to set my flash power. This is a long method and I wouldn't recommend it if you are pressed for time.
I learnt one important lesson during this shoot: Becareful when using an area with long grass in the warmer parts of our beautiful country. Snake activity tends to rise so you might find that you are not alone. We had a reptilian visitor and had to change the location rather quickly!! But we had fun nonetheless.
I hope this helps! And if any of you have some insight to share, don't hesitate. Your view is welcome.