Basically your outside, you want to expose for the ambient light whilst using a fill flash.
- use the manual setting on your camera
- you have to set your camera to the camera max shutter speed otherwise the camera won't see the flash (on my Canon it's 1/200 sec) 1/160 is normally pretty good to give you some room to move
- as you haven't much leeway on the shutter speed, the only way of letting more or less ambient light into your is by adjusting your aperture to suit
- adjust your flash power to suit the aperture
- adjust shutter speed to suit your image preferences i.e. slower to overexpose the ambient, faster to underexpose