Someone had a dream that some very bad things happened to his friend/relative/other. What should someone do after having such a dream? Is this is a sign of something? Perhaps one should do Teshuva? Maybe the friend/relative/other should do Teshuva? What can be said about having "bad dreams" about other people?
The person who had the dream should do a hatavat chalom with three good friends. It's found in some siddurim (I believe the Artscroll interlinear has it)
It should be pointed out, though, that the interpretation of dreams can be very counterintuitive and is in fact usually the opposite of what you would expect. See Shulchan Aruch O.C. 288, where a dream of someone dying is a good dream, seeing yourself getting married is a bad dream, and so on - so be aware that this may not be a bad dream at all according to the Jewish interpretation.