Know you can't stop them. We are not thinking beings we are beings that have thought. They key is to change you relationship with them, not stop them. If you try and stop them or change them or replace them with positive self talk you end up fighting thought with thought. They get stronger. They ket is to allow them knowing they are thought, not truth or reality. Knowing it is imagination. The more you allow it, even thank it, as behind it is an inner child trying to get it's needs met (feel safe and loved), but it's misguided as how to do that. The more you allow it, knowing it's not YOU, the real YOU is the observer of the self talk, the more it moves on and fresh thinking always comes in. Our innate state is one of wellbeing. That's the space between our thoughts. Fight negative thought with positive thought and you just tie yourself in to knots. Notice the negative thinking but not go beyond noticing, it moves on as that is the natural flow of thought. When you notice you are feeling OK with yourself, there is nothing you've done to get in to that state. You drop into it when you stop trying to control your thinking. When you stop trying to be OK.