Practising public speaking in front of a mirror is a bad idea. The concept is flawed because it focuses you on precisely the wrong thing: yourself. If you’re nervous, talking to the mirror will only make it worse, as you become more and more self-conscious. You’ll do a much better job – and feel more comfortable about it – if you remember that this talk is not about you, it’s about the audience.
Yes, it’s useful to be aware of your body language, but you can monitor this from the inside, without having to watch yourself in the mirror.
Clients sometimes mention that they need to be seeing eyes as they rehearse, both so they can practise making eye contact as they speak but also just to make the situation more realistic. I understand this but it’s not solved by staring into one’s own eyes in the mirror. A creative idea one client came up with is to gather as many teddy bears and soft toys as you can find around the house and make them your audience. (If you haven’t got any, perhaps you can borrow some for an afternoon.)
Another reason a mirror is unhelpful is that it distorts your view of the space you’re supposed to be commanding. You’re addressing yourself to the looking-glass world, which, as we all know, is a bizarre place inhabited by mad hatters and dormice.
By all means have a good look at yourself in the mirror before you deliver your speech or presentation on the day. It’s important you don’t go out there with your lunch down your front or one trouser leg inadvertently tucked into a sock: your appearance needs to be clean, tidy and undistracting, so check this is the case. That done, however, focus on the people who’ve come to listen to you – just as you did in rehearsal.