Just say no! If you know something is going to effect you negatively, why do it? Another less direct way is to try and change the subject. If the person preaching something bad to you doesn't really believe in what they were saying, they will forget about it. Next, you can predict peer pressure and leave the area. The last and most effective method is to use the buddy method, which means keeping a smart and confident friend close by ready to defend you and your decisions.
Ways to avoid peer pressure:
Avoiding negative peer pressure might seem harsh, even mean but it has to be done. If your friends try to force you to do something, chances are they don't even care about you. But whatever happens, you should not engage in it, innocent as it seems. A few silly decisions can change the way you think and affects the amount of thought you put into making decisions. For example- John has many 'close friends' and usually hangs out with them. Suddenly the young adult group gets into smoking. John is legally allowed to smoke and knows that it's bad. Should factors like legality effect his decision. What should he do? The point is that you shouldn't do anything which can harm you in any way.
Although there is a lot of negative peer pressure, positive peer pressure does exist. It should benefit you mentally, physically, emotionally or intellectually to qualify as positive.