I may be getting drunk/high with a friend in the near future, what are some things to consider and watch out for?

So this will be my first time getting drunk drunk, and my friend is a year older than me and has done it several times before. I could have him watch me, but there may be a chance that he'd be high/drunk too, so what are some things to watch out for and consider during my first time getting drunk if I'm able to go to his house?