Hopefully this is outside. Someplace just before or just after sunset you will have an exposure that looks great. About 10-15 minutes before sunset I'd settle in a place of where they wanted a prime photo taken form. I start taking some photos and walking it down (slower shutter, larger aperture) keeping pace with the sunset. At someplace your goanna loose the capability to handhold the camera and get clear shots (anyplace from 1/60 - 1/10, will work just the slower the more ambient light), pop on and turn on the flash - maybe about 20%, mostly pointed above the shrubs, and keep increasing the flash as necessary.