In short, everything. Clients are sometimes concerned about revealing personal facts for fear that they will automatically become part of the public record. What is more likely is that hidden information will not only be revealed by the other side, but that it will damage your case – sometimes irreparably – if your attorney was not privy to that information. The attorney-client privilege is inviolable. It is analogous to discussing a personal matter with the clergy.
The most successful attorney-client relationships are built on candor and honesty. So you should respond frankly to all the questions your attorney asks. Reveal information about infidelity, drug or alcohol use or addictions, police incidents and reports, instances of abuse or harassment, or incidents involving children that the other side might use against you.