Drugs, alcohol, cigarettes. They can all lead to addiction. Addiction can wreck your health and your life. Sometimes your friends can put pressure on you to try some of these things. But there are ways to say "no" and still be friends.
First of all, you have to make up your mind that you're not going to give in to this pressure. Know in your heart that you WILL NOT use drugs, alcohol, or cigarettes. This should not be hard to do. There is plenty of information about how harmful these substances are. Once you make a promise to yourself, it shouldn't be hard to convince others that you are not interested in using these things.
Next, you have to be consistent. Say "no" every time someone offers you drugs, alcohol, or cigarettes. The more you do, the more you will get your message across. You also will make your promise to yourself stronger. So, how do you say "no" and still stay friends? Listen in on these conversations:
"Hey, Bill, you want a cigarette?" Joe asks.
"No, thanks, Joe, I can't. I have football tryouts tomorrow. I want to be able to run without passing out," Bill laughs.