The safety aspect has been covered pretty well, but here are a few techniques I use with new pistol shooters:
I don't even bother to put up a target at first - let them work on the mechanics of grip, sight picture, pulling the trigger without anticipating the recoil, etcetera.
When you do put up a target, don't be afraid to put it close - I often start off at three yards. It's a big confidence builder for a new shooter when their first shots actually land on the paper (and often, close to the bullseye!). Nothing is more frustrating and less enjoyable for a new shooter than starting off at 25 yards and ending up with only a few hits. You can always move the target further out once they've begun to get the hang of it.