Quick answer
The safest sentence in the salon is Подстриги́те, пожа́луйста, чуть-чуть — cut just a little. Length is given in centimetres.
The basics
What you want done
How much
The appointment
Say the number
Russian stylists work with numbers, not gestures. Чуть-чуть means different things to different people, so follow it with два сантиме́тра. And не тро́гайте — don’t touch — is a perfectly polite instruction here.
Typical mistakes
мой во́лос
мои́ во́лосы
Hair is plural in Russian; во́лос is a single strand.
Я хочу́ стри́жку коро́ткий.
Я хочу́ коро́ткую стри́жку.
The adjective agrees and comes first.
Check yourself
Which is correct?