Many times teens will have to deal with situations and people that do not agree with their beliefs, values, and morals. It is important that in these situations, they are able to speak up for ourselves. Doing so is called being assertive. By being assertive, they are letting those around them know exactly how they feel and what they want out of the situation. By being clear about their thoughts and values, they will learn how to communicate their ideas better.
They have a right to express their opinions freely as long as they are respecting those around them. No matter how respectful and kind they may be, they will encounter people who will be aggressive, unkind, or disrespectful. If they encounter their peers acting this way towards them, they can choose to ignore them and walk away or be assertive in telling the person that they are being disrespectful and that they will not listen to what they are saying.
By being assertive and sticking to their morals, they will be less likely to be peer pressured or be put into situations where they will have to make bad or wrong choices. This means being able to say no to self-harming behaviors such as drugs, illegal activities, and drinking.
For more information on teaching your teen to be assertive, check out this article.