Basic NL Hold'em Knowledge Every Player Should Know

This article might unveil basics that even some experienced players never knew.

I think that all players should know about:

1. Outs and Probabilities - everyone (here) obviously knows this.
2. Hand Selection - You wouldn't play a 9-3 offsuited, unless you're PUI (playing under the influence)
3. Position Play

What I've listed is basic, and don't require much details, but if you list something that you think requires some elaboration, please do so... because it will make this thread rich! (and try not to be redundant)

Let's start!