I finally quit by using e-cigarettes which allow you to reduce the amount of nicotine gradually. Once you're at zero nicotine it's really just a habit that's quite easy to get rid of. One day you will forget your e-cigarette while going out and, surprisingly, it won't matter any longer.

It's important to switch from cigarettes to e-cigarettes exclusively and abruptly though. I have friends who tried to switch slowly and just ended up smoking both.

Once I used e-cigarettes I quit entirely within months. And it felt easy.