In doing outdoor portrait photography, I always try to either match (or exceed by 1 stop) the ambient light with a diffused strobe. You get the color of the sky (not blown out), and everything comes out nice and rich. It doesn't end up being too contrasty, and some contrast is actually a good thing or it will look "bland". While I happen to have battery powered units, you can use a regular on-camera flash (put it off-camera on a stand to get a more portrait look) shot through tracing paper to diffuse it. Grab your camera, flash, a stand, some tracing paper, and some friends - experiment for a bit and find out what works for you. Work on positioning, work on lighting, find what feels comfortable. Tell them not to wear anything white as it blows out in digital (don't know if you're using film or digital - just taking a chance there). Tell them not to wear any clothing with heavy patterns or very bright colors - it'll detract from their personality in the final image. As a nice touch, they could wear "like" clothing that is relaxed like jeans and all roughly the same color shirts. They can have different style shirts, but it'll still come across as unified. Side note - each stop up or down is double or half the amount (measurement) of light you give the exposure - hence "squared". Good luck and have fun.