Plain and simple - don't drink. You cannot legally drink or purchase alcoholic beverages in Pennsylvania until you are 21 years old. For the most updated laws on underage drinking in Pennsylvania, visit https://alcoholpolicy.niaaa.nih.gov/APIS_State_Profile.html?state=PA
If you are offered a drink, say no and make sure that they know you mean it. Don't be afraid to stand up for what you believe.
Avoid situations where alcohol is going to be part of the activities.
Never ever drive an automobile if you have been drinking. Also, never get into someone else's automobile if they were drinking.