i would like to apply for U-visa. what should i do first. i had domestic voilence before.

U visas are very unique. There are very specific qualifications and filing requirements to be met. You should consider hiring an attorney to review your case with you and determine if a U visa is appropriate. In addition to a U visa, if the perpetrator of the domestic violence was a citizen and you were married, you may be eligible for a VAWA self-petition. Please check with a lawyer prior to engaging in a course of action with CIS.