This is a situation many of us find ourselves in at many occasions. The Bible commands us to be wise in communicating with others. A few things that we must keep in our mind.
1. First we need to realise that while drinking alcohol and being drunk is a sin, it is not a greater sin than the other sins that we have in our lives. This will help us to talk to them in a less judgemental tone and communicate the truth in a more sensible manner. Most of the times, we tend to miss out some sins in our life while we are looking at the sins in others life.
2. Talk reasonably
Here are some reasons why we I wouldn't recommend alcohol to someone.
a. Alcohol is something that's addictive - this leads to drunkenness... Drunkenness is clearly condemned by the Bible. Why should I as a Christian, do something which makes it easier for me to sin rather than not sin? The rule is avoid sin and not play around with it. Not just Christians, but anybody should try to avoid things that are potentially addictive.
b. Alcohol has the capacity to destroy lives and relationships - Numerous families have been broken, children and women abused and much more damage has been done because of alcoholism. I would not want to promote the use of it, even by taking it in moderate amounts. For a greater good, that is helping people come out of such addictions and for peaceful homes - I'd happily not drink alcohol. It has a great potential to become an idol or evil - so I think abstinence is a more wise thing to do.
c. In a Christian perspective, This is a stumbling block to many. My total abstinence from alcohol is a great encouragement to someone who is trying to come out of this addiction or to not return to their old habit of drunkenness. (1 Cor 8:9-13) When I love God, giving up a type of drink - for the sake of my brother in Christ is something I would do joyfully.
d. It is harmful for the human body - that's why liquor bottles come with a warning sign on them.
3. Communicate the truth in love
Your friends should understand that your intent is not to condemn them, but to care for them. Avoid getting into unnecessary arguments while talking about the issue.
Remember that we cannot force someone to stop the drinking habits - whether they are occasional or habitual drinkers. Unless they don't get convicted about it - there would be no question of them giving up this practice. All we can do is give them the valid information, and leave the choice to them.
Also do watch the video in the recommended resource to get to know how Christians should view the habit of drinking alcohol. And from the Bible, I personally think there is enough reason to give up the habit of drinking.