It's great that you care enough to help someone quit smoking. It's important to remember that, in order to be successful at quitting smoking, a person has to be ready and has to do it for personal reasons.
Forcing someone to quit, or making them feel guilty about smoking just doesn't work. Lectures, nagging, guilt trips and put downs also will not work. Remember that the person is your friend/loved one first and a person who smokes second. What does work is being supportive and sensitive to their moods and needs, especially if they are trying to quit.
Give the person you are trying to help support, advice and your time to help them through the rough spots. Quitting smoking is not easy and every smoker/quitter is different, but you can help and there are resources that you can use.
Many people find it hard to stop smoking, but don't lose hope if someone you know quit before and started again!! Many people quit smoking every day and so can the person you care about! But only if they are ready.
It is very difficult for most smokers to stop smoking. The longer a person smokes, the more of their daily activities and moods become linked to their smoking habit and the harder it may be to give it up. Quitting smoking isn't easy but it is possible.