Using a word twice in a row isn't always a no-no, but there's always a more elegant way to revise a sentence in which you might initially be inclined to repeat a word immediately. When words collide, try these approaches:
1. "What you do do is your own business."
Even if this sentence is intended as a counterpoint to a "what you don't do" proposition, the emphatic first do is superfluous ("What you do is your own business"). If you must retain the repetition, introduce a separating phrase: "What you do decide to do is your own business."
2. "They had had many arguments."
Replace the second had with a prepositional phrase ("They had gotten into many arguments") or a more specific verb ("They had endured many arguments"), or introduce more vivid imagery into a revision ("They had verbally sparred many times").
3. "I showed her her message."
Replace one pronoun—preferably, both of the pronouns—with a noun ("I showed my sister the woman's message"). This isn't a problem with him, because two forms of the pronoun would appear ("I showed him his message"), though, again, if him and his refer to different men, it might be better to specify, in place of one pronoun or the other, one of the men in question.
4. "He came in in disarray."
Replace the prepositional phrase with a simple verb ("She entered in disarray").
5. "She gives in in every case."
Simply recast the final phrase ("She gives in every time") or flip the phrase to the front ("In every case, she gives in").
6. "What it is is a travesty."
"What it is" is always an unnecessarily verbose way to start a sentence. Start with the subject ("It's a travesty").
7. "I placed the card I had written on on the desk."
Recast the prepositional phrase "written on" with on at its head ("I placed the card on which I had written the note on the desk"). But first confirm that the modifying phrase involving written is necessary at all.
8. "We realize that that will not be satisfactory."
Replace the second that with a noun ("We realize that the proposal will not be satisfactory").
9. "We will discuss this this evening."
Replace the first this with a pronoun ("We will discuss it this evening") or a noun ("We will discuss the matter this evening").
10. "Is there someone I can talk to to resolve the issue?"
Employ a participial phrase in place in the infinitive phrase "to resolve" ("Is there someone I can talk to about resolving the issue?") or amplify the second to by replacing it with the phrase "in order to" ("Is there someone I can talk to in order to resolve the issue?").
Occasionally, an immediate repetition of a word, separated from the first instance by punctuation, is appropriate for emphatic effect ("I have come here from far, far away").
At other times, even though punctuation separates the repetition, a recast would improve the sentence. For example, "Even though I was there, there didn't seem to be anything for me to do" might be revised to "Even though I was there, I didn't seem to be of any use" or "Despite my presence, there didn't seem to be anything for me to do."
A version of this post originally ran on DailyWritingTips.com.