Watch some training videos and read more books on the subject to start.
Also carry some non lethal form of defense so you have another option in a non lethal stage of defense, like a fist fight or strong arm robbery without a weapon. It takes some time to become street savy. But you don't want to court danger either. You only shoot to save your life or prevent a crippling injury. You only have to be able to convince a jury of that so if in your mind, you are justified, then shoot. Have you read In The Gravest Extreme by Massad Ayoob? If not, get it and read it. When you are carrying, you must be in yellow alert mode... Spidey senses tingling... Yes, even feeling like you are a spy and every move you make, someone is watching you. That is the price we pay for carrying the power to take someones life.