This is my Dad last year at my Gran's 99th birthday meal. The room we were in was well lit but I don't think I had the 50mm lens then so the shutter speed was a little too long to be sharp. I'm not good at using flash indoors, I have the SB600 but I just don't use it properly. I also find in situations like this that the strength of the flash needed depends on how near you are to the subject and I forget to change the strength as I move around. Ad astra per aspera
However, you would probably have lost that reflection because the exposure would have been too high for it.
This guy is pretty good for on-camera flash technique.
But of course it all depends on the 'raydiosity' of the environment. You can't be me, I'm taken
For something like this I'd probably try bouncing it backwards and using the whole back wall as a diffuser. This confuses metering, so sometimes you have to set the exposure manually.
You can also buy clip-on diffusers which work fairly well and remove some of the hard edges, stark shadows and flattening.
Hand held flash can also work. Close the shutter as far as it goes, open it with a bulb setting for a second or two to add some ambience and movement blur, and manually fire the flash off the back wall.
Buying a crossbar support for the flash to move it off the lens axis also makes a bit of a difference. As a last resort you can use loo paper as a very cheap diffuser, but that's another good way to confuse the exposure metering.
