You might be surprised at how often admission officers spot exaggeration and outright lies in admission essays. An essay with such a flaw can quickly sink an application.
The best way to avoid getting caught in a lie is not to lie.
Don't discuss your friend's eye transplant (there is no such thing). Don't even change a sunny day to a rainy day in an attempt to heighten the drama; you may leave another detail unchanged that depends on the day having been sunny. Don't say that it was pitch black outside and then name something that you saw. Don't describe how amazing it was on a certain night, with the stars shining, if you were in a major city where you can never see the stars. The lesson here is that you or your editor must be a very strict fact checker, or a good detective. All the details of your narrative must be consistent and believable, both within the essay and given the rest of your application.
This does not mean that you shouldn't creatively interpret an experience. Remember that you can shape your readers' experience of your essay by drawing their attention to some details and not others. If you don't quite remember what people actually said and did, record what they probably would have said or done, on the basis of what you know about them--and that will be a genuine interpretation of what probably happened.
This advice also applies to what you have said and done. If you did a good thing, for instance, you can frame your action as a sign of a particular moral quality. The person on the Turkish minibus above, for instance, may have been a lot more afraid and a lot less courageous than the paragraph expresses. On the sentence level, note that most adverbs are the writer's own interpretations of an action, and adverbs sometimes can reinterpret events just enough to make your point without stretching the truth.