Hi, and welcome to the forum. I'm assuming they're beginners.
Hi / How are you / Good afternoon etc.
Sit here, please / Come here, please / Thank you / You're welcome
Phone greetings and taking reservations
Days of the week and times
Numbers and counting money
Hair / nail colours
Comparatives: shorter / longer / more curly / more straight
and the very important phrase: "like this" (as in "I want my hair to look like this")
This is going to take a number of classes and you'll also have the usual problems of teaching vocabulary and basic verb structures but get a coursebook for that and then the only material you have to make is the beautician specific stuff.