If I could go back in time, I would tell my younger self, "Get good at Street Fighter 2, so you can grow up to not suck at Capcom fighting games like I do now."
That way, I would not lose a million battle points every time I play Street Fighter IV online, and I'd actually be excited about this:
Also, I guess I'd tell myself to watch more Spider-Man cartoons so I would end up being a bigger Marvel fan to appreciate such a game even more.