For more naturally lit portraits, if the camera is held vertically and the flash is to one side of the lens, make sure it is on top.
A reflector can help remove shadow like fill in flash but is less harsh and more controllable.
Any white surface like a white panelled door can be used as a white back drop, put a flash on it.
Bounce flash. Direct flash can produce harsh flat lighting with unnatural shadows. Indoor natural day light with or without artificial lights will produce a more natural picture but could give low light problems. Bounce flash has a more natural feel.
A shower curtain can act as a big, cheap light diffuser.
Create soft flash lighting by simply taping some tracing paper or film over the flash. For best effect make sure the paper is not touching the flash but bowed out.
Off camera flash can give side lighting to a face or object to give the picture more depth or a 3D effect.
Off camera flash. The flash gun can be triggered by the main flash if it is fitted with a slave. The limitations being loss of TTL metering, range of cameras main flash, not woring in bright light and being triggered by another cameras flash.
Off camera flash. By using the camera, flash gun and a flash lead the cameras TTL metering can be kept. The only limitation being length of lead.
Off camera flash. By using the camera, flash gun and a flash trigger and receiver(s). This system needs to be quite expensive to maintain the cameras TTL metering.
The flash fires at such a fast speed it will freeze action. It also fires at such a fast speed that that the camera shutter speed will not affect the flash exposure. Whether the exposure is 1/200 of a second or 30 seconds, the flash exposure will be the same. The only thing that the shutter speed will do, is alter the ambient light. To alter the effect of the flash output the f stop or ISO will need to be altered. More ISO is more grain/noise. By setting the camera to around f8, you can go up or down on the f nuber to easily change the effect of the flash.