The light produced by flash is bright and intense; before you take your picture, consider carefully whether using flash is really appropriate for your circumstance. If you're photographing light sensitive objects (or people) abstaining might be a better idea; adjust ISO settings and utilize other techniques to replicate the same effects.
Also, make sure that you correctly adjust ISO, exposure and other options on your camera to account for the additional light. This might be difficult at first, so taking your camera out for a few shoots just to see how strong your particular flash is, is probably a good idea so that you know how much you'll have to adjust your settings when the time comes to use flash.
Some cameras and/or flashes will have something called ETTL, which essentially will make many of those adjustments for you. However, these will often have as many difficulties as adjusting the settings for yourself. It is best, as always, to experiment with such.
Without further ado, the two main outdoor flash techniques: