Substitution and diversion can work. However, it can also be useful to try to identify why the thought is amplified. For example, If someone said something rude to you, you might hold on to it thinking of what you might have said or done in response. these sort of thoughts can be minimized by reflecting that the person is a jerk and what he says should be expected to be hurtful.
Some thoughts are held onto sort of as self-punishment. Others can be held because they provide a sort of emotional intensity. Intrusive thoughts can also be bothersome. One might be able to slowly develop an ability to take control of the thought process by first working at the fringe. If an occasional peripheral thought comes up, you might counter with doing multiplication tables.
In the movie "New Leaf" Walter Mathau comments that he could engage in any romantic activity with an urbanity born of disinterest. That line captures a little of the world weariness that a consumptive or jaded life can bring. Those who struggle more to make a living or seek ways to help others can find that their level of activity tends to allow little opportunity for thoughts to grow out of proportion.