A good personal reference is always the best. Short of that you should do your homework do your investigation, your evaluation of your lawyer. You want someone who has a track record of success, practices regularly in the area of law involved with your particular injury case; if it's a motor vehicle case, products case, an engineering case, a medical malpractice case. Find out what experience they've had handling similar cases and also satisfy yourself that the firm can bring the resources to bear that are going to be required to properly present your case against the forces that are going to be coming at you from the other side, which, now a days are considerable.
99% of our injury work is against insurance companies who are in the business of defending cases who have not only an army of lawyers, but an army of consultants, to throw against you and you really want someone pulling for you who can fight that fight.