Then, whenever the temptation arises to think about these topics (which it will), quickly dismiss the thought and turn your mind to God, for instance by repeating a line or two from a favourite prayer.
Try this for 30 days.
Emmet Fox's original writing on the matter:
Stand By For Quarantine! (Emmet Fox)
When you are praying or treating about a particular thing, you should handle it, mentally, very carefully indeed. The ideal way is not to think about it at all except when you are actually praying about it. To think about it in between, especially to talk to other people about it, is exceedingly likely to invite failure.
When a new problem presents itself to you, you should immediately know the Truth about it, and then decline to consider it except in the light of Truth. I call this ‘putting a subject in quarantine,’ and whenever I have been able to ‘quarantine’ a problem of my own I have always demonstrated very easily and very well.
Even and old, long-standing problem can be ‘put in quarantine’ today, if you mean business and will resolutely break the habit of constantly thinking over that problem.
Everyone knows that a photographer must not expose unfixed film to daylight if he wants to get results. Everyone knows how careful a chemist is to isolate (i.e., quarantine) his materials in the laboratory, since the slightest contamination of one chemical by another will probably ruin any experiment. What many Truth students do not seem to understand is that mental operations have to be just as carefully safeguarded if demonstrations are to be made.
Whenever you think about any subject, you are treating it with your thought—either for good or evil.
 Sin [= "missing the mark"] is a sense of separateness from God, and is the major tragedy of human experience. It is, of course, rooted in selfishness. It is essentially an attempt to gain some supposed good to which we are not entitled in justice. It is a sense of isolated, self-regarding, personal existence, whereas the Truth of Being is that all is One. Our true selves are at one with God, undivided from Him, expressing His ideas, witnessing to His nature—the dynamic Thinking of that Mind. Because we are all one with the great Whole of which we are spiritually a part, it follows that we are one with all men. Just because in Him we live and move and have our being, we are, in the absolute sense, all essentially one.