What would you tell 16 year old you?

I'd tell myself to be more "careful" with the people I wanted to be friends with; most of them were terrible influences back then, and most of them were actually older than me. I actually had to stop myself from hanging out with some of them when I got much older, so it could save some time and bad experiences. The few friends that I still hang out with I feel more comfortable with, despite being a wreck when we were 16, we actually grew up and we aren't so damn stupid anymore.
I'd tell myself to try and keep a cooler head when horny. To this day I still regret hooking up with girls I didn't like at all... and I regret it so much more when those girls actually liked me and I just took advantage of it. As for girlfriends... I don't regret much, other than stupid mistakes that can't be avoided everything went okish with them so I wouldn't say anything about it.
I would tell myself how to deal with school, since I hated it but found a way around it (when I was 18 -_-) that wouldn't stop me from getting into college. But I'd also recommend getting a job to not become a lazy pineapple. As for gaming I'd tell myself to avoid mmorpgs in general, especially "f2p" shits that have no value whatsoever. I'm ok with how I've dealt with family all along.

That's about it.