The Work of Byron Katie
Very very good
It also helps to try out many different techniques to see what works for you. I generally attack something from all angles and all tools from my personal / spiritual dev. toolbox and see what's most effective. Sometimes it takes multiple tries, multiple techniques, multiple approaches -- which can be frustrating (or challenging, depending on how you look at it
).
I most generally use a variant of the Sedona Method, which is to surrender with your whole beingness to the negative energy/karma underlying the belief and gradually dissolve it through awareness / surrender / forgiveness / prayer.