The role of L1 in L2 setting

Hello,:)

This is Gul Destici from Izmir-Turkey. I have been teaching English to teenagers from all levels of proficiency in my country.After 16 years of experience, believe I still need to learn many things relating to the field we are working in, .I would like to start by opening a discussion on the following subject=

What do you think the role of L1 in teaching a second/foreign language should be?