It is difficult to understand the answer to your question if you have only ever spoken English. However, through studying Spanish, I have started to understand the difference between the imperfect past tense and the preterite past tense.

"Where did you used to live before you came here?" would be the correct form of the two (provided that you said 'used' and not 'use') because it is the imperfect tense, referring to something that happened for a period of time.

I like that you mentioned the possibility of "Where were you living before you came here?" because it stands in the overlapping area of the past progressive tense and the imperfect tense - in Spanish, the past progressive can always be a substitute (though sometimes awkwardly) for the imperfect tense. In English, however, this overlap may not be as large.

If I may extend this, unlike what Warsaw Will said, "Where did you live before you came here?" is incorrect, as it is asked in the preterite tense, which is only used to refer to specific points in time. In other words, you would be asking where the person was living at the point in time just before they 'came here'.