Theres no great answer to your question. I would say make sure the person is a member of AILA (American Immigration Lawyers Association). Make sure they explain whatever options you have and the process and don't make you feel pressured to proceed. Make sure the person returns your calls. Make sure you understand all costs up front and are given a fee agreement to sign. Meet with a couple people and hire who you feel most comfortable with. Marriage based AOS when the beneficiary has an arrest record is standard enough that most immigration attorneys have experience with it. Good Luck.
Massachusetts Immigration Attorney
If you go to www.aila.org you will find an immigration attorney referral service by clicking on the link entitled "Find a Lawyer." It is very important that you ask the attorney if they have experience with criminal immigration issues. If they do not, perhaps they can refer you to an attorney who does.
This is hard sometimes. But most people base their decisions on a consultation. When anyone comes into my office they immediately know that I have handled many of these cases as I am answering their questions and interacting with them easily. I have few unknown answers and try to put them at ease. But your case will all depend on what you were arrested for. hopefully it was minor. Otherwise you may need a waiver which gets tricky sometimes. Good luck. We offer a free consultation if you want more assistance from us.
Start with recommendations from relatives and friends. Research the attorneys' profiles online to make sure that they are qualified and make sure they have not been disciplined by the California State Bar: http://members.calbar.ca.gov/fal/MemberSearch/QuickSearch. Schedule consultations with the attorneys that you are most interested in working with. Make sure they have experience with handling marriage-based petitions involving criminal records. Make sure you understand their fees and terms. Feel free to ask the attorney any questions you have. You want someone who is not only competent and experienced, but also someone who returns your phone calls and e-mails promptly. If you don't feel completely comfortable with someone, don't go with them.