I guess the goal for reducing alcoholism around people you know is making alcohol less accessible when your friends and love ones are around. This does not cause them to crave alcohol, but in some cases, it ties family and togetherness with sobriety.

However, it has to be a two-pronged attack: you have to reduce the amount of alone time your friend is spending by himself. If there are weekends or evenings when there is nothing going on in your friends life while he is at home, you visit him or call him. It's kind of tough at first, but usually people give warning signs as to whether or not they feel lonely. Try and be receptive as to when they want to hang out, and though it is difficult, try and make it possible to change your plans to include your friend. Even if it is just a trip to the store.

I think what gets to most people in the military is the isolation from friends and family. You have to make an effort to reduce the feeling of aloneness at home, and that may curb your friend's habits from duty.

That's all I can think of, anyway. Works for college students, too.

@jhim43 - 

Thanks for the advice. I guess I probably should have mentioned that he's not a confirmed alcoholic or anything like that, but he talks a lot about drinking, and does a lot of drinking, most of it so far seems to be socially though. My biggest thing would probably be to get him away from places where alcohol are though. He's still technically underage, so it's hard for him to have access to it, unless he's at a place where someone else has bought it for him. (I've been the person they've attempted to persuade into buying alcohol for several times.) I hate it when people are interacting with me under the influence of anything (weed, alcohol, etc.), so when we do hang out, I'll make sure there's nothing around for him to drink, so that maybe I can start telling him that he needs to hold off on so much drinking, because it could totally ruin him if he did actually become an alcoholic.