I quit smoking successfully a few years ago, after at least a dozen unsuccessful attempts.
Here's what was different the time I succeeded:

I changed my mindset. Basically, I told myself that I won't ever smoke a single cigarette again in my life, no matter how shitty that makes me feel.
The trigger for that mindset was a common cold that left me breathless for 4 weeks.
And the key to success was the realization that:

1.) I'm not addicted to cigarettes, I'm addicted to nicotine
2.) Nicotine by itself isn't all that harmful
3.) Whenever I have a craving, I can just chew a nicotine chewing gum
4.) Nicotine by itself isn't even that addictive

So I bought a whole lot of nicotine gum, and whenever I felt the slightest craving I popped one in.
After about 2 weeks the cravings subsided (cause nicotine isn't actually what makes you addicted).