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As mentioned, someetimes you may want to drag the shutter or up iso a bit to include some ambient lighting in the background. Also, if on camera, bouncing is ideal. I tend to zoom the flash to 70mm or so, and face it at whatever wall or ceiling seems closest or is whitest. I've had luck bouncing off corrugated aluminum ceilings, grey stone walls, wooden gym walls, and even concrete floors though, so don't be afraid to experiment. Just keep in mind the surface you're bouncing from so you can adjust flash output as needed. It really becomes second nature after a few hours. Personally though, I tend to dislike the look of bounced flash. It beats direct flash, but it still creates a distinct look. Whenever possible, I like to get the flash off-camera and into a modifier like an umbrella.
With shutter speeds, be careful not to excede the sync speed. I know with the 5d3 that's 1/160s, but the classic might be better. Speeds faster than the max sync will leave a black bar in the bottom of your photo.