Only fired indoors once in my life. But, whether indoors or out, I always use both plugs and muffs. I have electronic earmuffs, which I turn all the way up when I've got my plugs in. I can hear normal conversation pretty well, but no fear of concussion and muzzle blast.
Even with both, I always stand back a ways when someone shoots with a break. One can never be too safe, and I want to keep my hearing for as long as I can.
-Patriot