Observe what is interesting and process it.
Question everything, think, then form your own opinion. Change as needed – this part is important.
Always keep an open mind and stay alert for opportunities where you were wrong – this means you get to change your mind, which is proof that you are growing!
Mostly, though, just pay attention. If you do so, life will teach you much of what you need to know.
Oh, and don’t be an asshole. Seriously – if nothing else, at least this is in your control.