Depending on the age of the child, you must consider your approach. Truth is always best. For starters, arguably alcohol is the last legal drug available to anyone over the age of 21 in most states. It is toxic in high doses. Some people manage drinking high amounts of alcohol for a reason. It is legal for a reason and most people will try a sip or more in their lifetime.
When your child is very young, you must open the discussion of alcohol. When they are at a wedding or an event like a dinner where someone else is drinking, you must let them know that a drink or two is permissible in society and that most adults can handle one or two drinks. It exists. This plants a seed.
When children attain middle school age where their peers are discussing and possibly sneaking booze into school, a new approach is needed, such as "just because Sally and Johnny can bring alcohol to school doesn't mean it's okay to participate. You must make decisions for yourself and you must make decisions that don't have a negative impact on others in your community. In other words, drunk drivers are responsible for damage and death (if it occurs) because they could not or would not stop drinking before they became intoxicated." This is an appropriate age to talk about repercussions of poor decisions.
By the time your child has reached high school, he or she has been exposed to alcohol either because a friend brought it, or a group got together and they got it at a party or social event.
I was able to talk to my children about the dangers of being an alcoholic because it runs in the family and both sides of the family have suffered from excessive abuse. It was necessary to have the discussion early about knowing that if a disease does run in the family, that there is a likelihood the child may experiment and it prove dangerous. Further to that discussion, we engaged with family members who overcame their abuse and how long it took them and what had to happen before they sought help. Reminding children that it can happen to them and that it doesn't always happen to someone else is vital to having an impact on them so they can make better personal choices.
Finally as they go off to college, there is the reminder there is an increase in deaths among college age kids because they now finally have the complete freedom to make random choices and so many are not used to alcohol and overindulge in order to be part of the cool group. Beware: acute alcohol poisoning.