This was one of my first experiences using an off-camera flash. I recommend this technique to anyone who is eager to unleash his/her creativity. It brings a lot of possibilities, much more than using the external flash on camera.
Minimum required equipment is: a camera with commander and an external flash which can be used as slave (commanded by the internal flash of the camera). A tripod can also be very useful as in macro photography achieving focus by using the camera handheld can be quite cumbersome. Also a flash diffuser can be used to get a softer light.
The external flash can be put in a fixed position (e.g. using a tripod) or can be handheld (while the camera is on a tripod). By handholding the flash you can easily change it’s position until you get the required lighting effect in the picture.
Depending on the application one or more external flashes might be used. As I had only one I also used the internal flash to get more lighting (fill flash).