The first and most important thing is you have to want to quit. Don't pick a day, or after you finish the rest of the pack. Don't say you will quit after you get past your current emotional (or other) problem. You have to decide you have had enough and not one more cigarette.
When you need a cigarette, tell yourself you quit. Yes of course you want one, but you can't have even one. If you have one then you haven't quit. There is absolutely no in between. This goes for more than just cigarettes. This is how I quit and its been eight years.
It helps to have a reason to quit. For me it was
my throat bothering me and being told it could become permanent. It may
be your health, your families health (second hand smoke or picking up your
habit), the cost of smoking (almost $1000/year at two packs a day), or
you notice your clothes don't have that fresh clean scent even after washing.
For almost anything in your life you want to change you need a reason.
You have to want to change. It may hurt but it is always worth it. It also
can help to find a friend who has been through the same thing that you
can call when you have the urge or just to discuss what you are going through.