There are lot's of other great blogs that discuss flash techniques, so I decided to reference them here. The things I put in my blogs are extensions and amplifications to things I have read in these other sites plus additional things I have discovered during my wedding and event photography.
Neil van Niekerk is a wedding photographer who uses both Nikon and Canon speedlights and describes his methods for making the lighting from the flash subtle and with a natural appearance.
David Hobby describes the equipment needed and dozens of ways to use speedlights off-camera. I highly recommend you read his blogs under 'Lighting 101'.