Just to echo - what an excellent thread.
When practicing make use of video cameras or even PC Cameras. They are far better than mirrors for showing you what you look
and sound like from the spectators perspective. Keep to wide shots rather than where the action is taking place as this will possibly reveal a lot more about your stage presence than merely the ability to accomplish a trick or effect.
Very obvious but sometimes the obvious is the first to be overlooked; do not test or try out your new feat until you are 100% happy with what you are doing. There is nothing worse than something going wrong or being accidentally revealed because of lack of practice or sudden bout of nerves. Ensure you are confident in what you are doing before going public.
Do not be shy about making eye contact with people. Look at their foreheads if that makes you more comfortable, they won't notice the difference. Also ensure you scan your audience regularly as it makes tem feel more included and appreciated.
Your volunteer(s) are important so make a fuss of them, remember their names (repeat it each time you talk to them if you have a poor memory as it will help it stick). Thank them when they volunteer and when you are releasing them, if appropriate incite a round a of applause for their help.
When using volunteers remember that you are not performing to them but the audience. Slight difference with some mentalism but even then don't forget those looking in.
Brush your teeth, use mouth wash, chew mints, use soap & deodorant. fairly obvious but I bet we've all encountered people who have 'forgotten'.
Especially when working with children or if you are tall check out those nasal hairs. I've seen a few student teachers cut right down by a little kids 'innocent' comment.
Enjoy yourself. If you are not having fun you need a new hobby or profession.
Never allow yourself to believe that you can't be taught something new by the most recent beginner no matter how long you've been doing something. Chances are that you probably HAVE forgotten more than they know but one of those things may be important or they may have a fresh insight. Learnt not via magic but I regard this tip as very important.
Think about acting and use of your voice. Perform your magical feat rather than simply show or do a trick. Be prepared to improvise too.
Rabbits and other animals (including children) are the natural enemy of the magician!