My internal dialogue blathers non-stop.
Here is what helps to maintain a bit of silence:
Meditation (I recommend practicing meditation with real buddhists for best results)
Breathwork (Breathwork is the opposite of thinking, its hard to think when you are truly in a state of breathwork)
And you can consistently tell yourself to "shut the f- up" when you find yourself being too noisy. This is an effective mantra especially when chanted aloud.