Student or Learner
When I go to the barbershop to have a haircut. The hairdresser asked me how short I want to be something like this.
I do not know how to say? What are the common sentence used in barbershop for you native speakers?
not a teacher
What you say depends on what you want.
If I want the barber to just tidy up my hair and not cut off too much, I might say something like, "Just a trim please, not too much".
But you might want to give more precise instructions.
"Quite short at the back and sides, but leave the front as it is."
"I'd like it a lot shorter all over, but keep the sideburns."
"Leave it long on top, shave the rest off."
As I say, it depends what you want.
As Mike suggests, a picture might help avert a disaster.
Here's a very thorough guide: Hudson's Guide: Men's Short Haircuts and the Barber Shop