Tip: don't make a grand "this is my last cigarette" moment - that cigarette will be the best tasting cigarette you've ever had. just randomly throw out your pack. toss it into the next garbage can you see.
Then you need to do two things: remind yourself that you're the one in control. you're the one who chose to quit, and if you smoke again, you're the one choosing to smoke. so consciously choose not to smoke. the second thing, figure out what you'll do instead. if you smoke during times of stress - what will you do now? if you smoke when you're bored - what will you do now? if you smoke when you're being social - what will you do now? plan ahead
the hardest ones for me to give up were the ones in the car, i loved driving and smoking, so i had to figure out what to do instead. for me, i had to have something in my hand so i bought a spinner ring.
also, take the money you were spending on cigarettes and have it automatically put into a separate account. then every few months, use that money to treat yourself to something