How can I stop smoking?

Cigarettes. I started the habit about four months ago, and I can't stop now. I'm only 18, but I want to quit before it turns into a lifelong habit. I'd rather have someone answer this who has successfully quit smoking. Please give me some helpful tips that can help reduce cravings. I completely underestimated the power of addiction. I have half a pack of cigarettes left, and I'm tempted to break them and throw them away.