Meet the The British-Iranian cellists Leila and Sara Shirvani

Sit tall in a firm chair. Get a firm chair to sit in that allows your hips to be slightly higher than your knees. Sit with your back straight and tall; imagine that a string is attached your head and it’s pulling your head up. Engage your tummy muscles to straighten your spine in your lower back.

• As you play, use your eyes to look at the strings. Try not to drop your neck to avoid injuring your neck in the long term.