While Brett doesn't maintain his blog anymore, the archives are worth the visit. For those thinking of trading (or already trading) this is one of the few resources where the mental game of trading is addressed.
To me he is the foremost expert in Psychological aspects of Trading.
He has a wealth of articles containing information on being a better trader by studying yourself. Know yourself, know your system. Take keeping a trade journal. He has articles about the importance as well as how to set them up and metrics to use. He goes into what language inside helps, which hurts.
Great stuff. I have a collection of his writings called the Best of Brett Steenbarger, I recommend other people at least give him a perusal.