Take every thought captive.
There is a difference between our conscience - the thoughts that remind us where we have spoken harshly, where we have been less than forgiving, where we need to seek forgiveness - and those lies that jab at us and insinuate and cause us to question those things that just happen through no fault of our own.
Each thought needs to be weighed and considered. Is it true? If it is, what do I need to do about it? If it isn't, why am I giving it room in my mind?