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I work at party and events.
So, you need your flash to bounce, don't make it direct to the subject, even with diffuse or softbox (believe me, there are some people going to parties with heads softbox).
You need your background to be well exposed to0, but, you'll need a very low noise! Time to low your ISO to your 'ok measures', I like to let it between 100-1600, some very hard occasions, higher because of really dark background!
Because of your low ISO settings, you will need a lower shutter speed also, it's your taste, mine is about 'bulb' or 1/10 (I like light painting), "but, wut about muh sharpness?" relax kiddo, the flash will do it for you!
Set your flash to -2 TTL or just, give it some manual tries.
Before you turn on your flash, give some shots until you find a nice background, them, turn on your flash and set it to your tastes. remember of low contrast give you better skin tone.
Protect your camera from all the boose that are going to fall on it.