I have the same problem with social anxiety, and alcohol and cigarettes at gatherings with friends. For awhile I would always drink way too much due to anxiety, but normally if I'm not in stressful situations I actually prefer not to drink.
I find if I have something to focus my energy on, like focusing on the cigarette or the smoke when I'm talking that I get more relaxed. I also find that the thing with smoking, is you can go outside and have a moment alone. I do get social ticks, like I touch my hair too much, or start touching things, or looking around and getting distracted. This happens mostly when I am uncomfortable talking to whoever I am talking to.
My biggest problem with social gatherings is the pressure to perform, and my Fe goes in overdrive, and I usually need a moment alone to activate Ti.
This being said, I have begun to realize that most of the other intuitives that I hang out with have these same social anxieties, and that it kind of lessens the pressure that I experienced in the past. I do know that certain friends of mine seem to trigger more intense anxiety. I have this one friend who is a sensor, and I feel really self-aware when I am with her, because my form of communication is so unnatural to her. After I leave hanging out with her, I feel way better, like a weight has been lifted, although it usually takes longer for me to recover from my hang out sessions with her.
I used to think that I needed a lot of alone time after social events, like a week, or at least three days to process, but I've got it down to a productive hour or two where I analyze the events and move on. Writing in a diary really seems to help.
I think the biggest part is visualizing a successful outcome in those situations ahead of time, setting limits, and then not allowing myself to worry or second guess myself. I hate the agony of over-analyzing situations long gone by.
In addition to visualizing the best possible outcome in social situations, I also think of the worst case scenario, say aloud what the worst possible thing that could happen could be, realize how silly it is, and then move on from there. I try to look at my thoughts objectively and think what I would say if it was a friend of mine having these same doubts or thoughts. What would I tell someone who says they are not good enough for the people at the party? I would tell them, relax and just see what happens. Then that is what I tell myself.
I also take deep breaths before I join the party, and remind myself during the party to stay calm. In addition, if I'm really not feeling sociable, and it's one of those situations where I have to go, then I will take some reading material, if the party is totally boring I will read a book or read on my phone. I realized that instead of assuming that I'm boring, that maybe the other person is as well, or try not to make judgments on my mistakes, or make judgments on the person that I am talking to. It makes it a lot harder to have a good time if you've judged everybody in the room and decided that they are not worth your time, or that you are not worth their's. I don't know if that's an INFJ thing, or if that's just something I'm prone to doing.