Outdoor shots like this, even in daylight, still require additional lighting. Not having additional lighting means underexposed parts of your shot.
For this shoot, I used my Canon 580ex flashgun, with a reflective umbrella on a stand. I had someone holding the umbrella in the high wind (if I don't have someone, I do carry soft ankle weights, which I attach to the stand bottom to weigh it down for outdoors shoots).
The reflected umbrella gives the beautiful catch-lights in this model's eyes, while providing nice, soft directional light. The light--moderated with a CTO (color temperature orange) flash filter, gives a nice, bronze hue to the model which complimented the setting sun.
For any of my shoots, I always use wireless setups, so there are no wires to bundle and trip over. After experimenting with very inexpensive wireless triggers from China, I have found that you get what you pay for; my bargain gadgets let me down too often, failing to fire or operate at a shoot. After doing some research, I have found and settled on the Paul C. Buff Cybersyncs. These transmitter-receiver rigs are extraordinarily reliable while being affordable. If you're just starting out, check out their site ( http://www.paulcbuff.com/cybersync.php ). You need a transmitter to go on top of your camera's hot shoe, there the flash would normally go, then one receiver for each of the flashes you plan to use. You set your flashes on the "slave mode", and as you take your shot, the slaved flash will fire, even if you don't have line-of-sight (or they will if you use a decent unit like a Cybersync or a Pocketwizard).
You can do as I did, and experiment with the very cheap gadgety-triggers, but I have found that they work briefly and then crap out. They're dirt cheap, so you get what you pay for. I have read web reviews by those who swear by the inexpensive triggers, as an alternative to the more expensive but rock-solid Pocket Wizards or Cybersyncs. My decision to use Cybersyncs was based on failures of cheaper units; I cannot go to a shoot and be fiddling with remote flash triggers that keep failing.
Once I have your modelling shoot planned out (general structure as to where I want to shoot, what "look" I'm aiming for, etc), I generally will use two soft-boxes with Canon 580ex and 480ex respectively at 45 degree angles to the model. I'll supplement this with a third flashgun straight-on to the model, a Canon 320ex mounted in the reflective umbrella rig (sometimes I'll set it up as a shoot-through umbrella rig for softer, more diffuse light). I can also use the modelling light on the 320 unit, attached to a Gorrila Pod overhead to act as a nice hair light ass well.
And a quick word as to the lens; for almost this entire shoot, I was using a Canon 85 mm EF prime lens. I love this lens, one of the best for portraiture I have found. Owing to the fact its an 85 mm, however, you will need a fair bit of space to frame up your shot. A prime lens is one which does not zoom or move. In other words, you look through the viewfinder, and what you see is what you can shoot; to re-compose your shot, you need to move, you can't adjust the lens to re-compose your scene. This makes things a tad awkward at times, but the benefit is that a prime lens--with no moving parts--can have a much larger base aperture (faster lens, which means it can admit much more light into the camera, so you can take low light shots without a flash or tripod, as well as creating beautiful bokeh, or background blur, by using the widest aperture setting).
A prime lens is also capable of capturing images that are tack-sharp, with vivid colors and next-to-no distortion, flare or other lens abberations. When looking at this shot, you can see the buttery-smooth texture of the image aspects, the sharpness of focus where it counts, the beautiful background blur (bokeh) made possible by the very wide aperture. In fact, to get this de-focused background, I opened the aperture to its largest setting of f1.8, then used a four-stop neutral density filter to tame the incoming light to prevent over exposure.
To see more photos of this beautiful model from this shoot, please go to my website page and click on the portraiture page.