The longer you smoke the worse it is so you should quit immediately.
There are a couple of different ways you can quit. You can go cold turkey or you can use quit aids such as nicotine patches or gum.
To keep yourself motivated you should think about why you want to quit (eg for health reasons, to save money, because it's annoying to have to go outside for a smoke etc). Also, inform the people around you of your intention to quit as they will give you encouragement and won't offer you cigarette's.
There is information available to you so that you can increase your chances of quitting successfully. In Australia there is a telephone service call the Quitline which provides smokers with information about how to quit. You should see if there is a similar thing in your area as these sorts of things are really good resources. They can send you out some brochures and give you tips about quitting.
It's great that you want to quit since smoking is associated with a huge number of health problems including a variety of cancers (lung, mouth, throat, bladder), emphysema, bronchitis, pregnancy-related problems, heart disease, stroke and harmful effects on others through passive smoking.
If your attempts to quit are unsuccessful see your GP for further advice and options.
Good luck with it!