Even though I don't read often, I have read on 4 or 5 occasions at psychic fairs. in the last so many years.
Take bits and pieces with you that let you feel more at home in the often alien or sterile Fair surroundings. For example, I always used to take two easily transportable comfy chairs, draped with fabric so they looked like lounge chairs, and a small round table draped with fabric, too. I took a bell to clear the space, because you cannot have candles or smudge in many places (insurance!), and a table lamp to cover poor lighting, plus a few ornaments. All of this made a boxed in stall-like area look like a cosy lounge room, allowing for a much more intimate space. One young woman asked if she could just come in and sit... she was literally JUST out from her boyfriend's funeral, across the road, and her friends wanted to attend the Fair. She just needed a cosy space! I gave her a free, nurturing mandala and no reading... I could see she wasn't ready for one... but that space gave her comfort and also encouraged many others to just come in and most had readings. A woman at the next table was the Fair organizer's lovely wife. She was very confident and coul call people in, physically call them.. I am quieter by nature, so did no calling, but my set up welcomed people, and I did pretty well as a newbie
Also, stick to your guns... If the cards tell you a story, even if someone is saying "No, that's not it", if you fell clear within yourself that you are reading correctly,stick to your story. I had one such person refute everything I was saying... as it turned out, he was testing me, to be sure, because the cards were telling him sonething he wanted to hear, but he really needed to know, as the outcome involved relocating from one corner of the globe to another (I didn't knwo THAT, and I just knew what the carsd were saying). He was my most difficult client, and one of my most cherished experienecs, because I did stick to my story...
Be amenable, wherever you can... I had a couple of people who were rushing... couldn't do a full reading and just wanted a quick sweep... I gave them a speedy 3 card reading, just the basics, which they enjoyed...
Also, it helps if you take a notepad (with time slots printed on it) and pens, so that people can jot down an appointment, even as your are working with someone else, and come back for their designated time slot... People at Fairs are generally there because they want something, and they want it now, and you'll get more custom if people can reserve a place and fill in their waiting time looking around the Fair rather than queing to attract your attention...
Enjoy it... being stressed blocks your capacity to read... stay calm, breathe deeply, know that you are there offering a service, and you cstomers are there to share your insights.
Yes... as others have mentioned, drink LOTS of water... Lots....
Have fun!