Grahm,
You have already gotten such excellent suggestions. You are a polite, humble and gracious person, and that is what is most important, and people - especially elderly people - will appreciate and treasure that. I am sure that they recognized that in you when you did your first show.
The suggestions I would add are as follows: Tell yourself that this is going to be fun, and work on keeping that mind set now and all the way to and through the show. When you project an easy-going, relaxed fun-loving attitude, people will pick up on it and have fun too. You will enjoy it too and get good at ridding yourself of at least most of your apprehension or nervousness, which will serve you well as a performer going forward.
If you know a good joke or two, you can insert it/them in between routines, but if there are hearing issues, it might be a good idea to see about amplifying your voice, as Maaz suggested. If that's not possible, be sure to project your voice and to speak clearly and slowly.
If you don't already do it, you may want to consider bringing volunteers up to help you. Ask the audience to give them a nice round of applause as they come up and when the trick/routine is finished. When they first come up ask them about themselves, where they are from. This usually enhances the interest-factor and the entertainment. They themselves will often say or do funny things.
Finally, I don't know if you have a Magician's Insurance Policy, but they are very cheap to pick up on Amazon. With a simple cross-cut force or other basic force, you will have an effect that plays quite big when that big colorful picture of the playing card is revealed at the end. Meanwhile you can play up the Magician in trouble theme, e.g act like you are trying to read their minds and fail by getting the wrong card, and then maybe fail again after looking through the deck with a concerned look, making comments such as, "this isn't going to look good on my resume," or whatever suits your personality. You can make comments such as "I hope my premiums are paid up on this policy," or prior to unfolding it all the way, you can pretend you are reading from the first page and say, "Let's see, it says here that all parties must be playing with a full deck - I guess that counts me out "or Hmmm it says that their friendly claims agents are always ready at all times to help me with a claim, anytime of the day or night...except on Monday through Friday and weekends." You can milk a lot of entertainment out of something that packs so small. Just some suggestions. Good luck and enjoy!
