If you hire a lawyer, make sure your lawyer is an experienced bankruptcy lawyer. Bankruptcy is a complex, unique area of law that is not something that a general practitioner can learn overnight. Ask your lawyer how many bankruptcies they have filed.
Your lawyer will probably have you fill in a questionnaire about your property, debts, expenses and income. A good lawyer will be able to determine quickly what kinds of debts will be dischargeable in bankruptcy. The lawyer should advise you to get credit counseling before you file, and will may even have a computer terminal in their office where you can do the counseling right there, online. Many lawyers have preferred credit counselors that they work with.
Lawyers are responsible for making sure that your information is accurate, so they will be asking you to bring in documentation about your finances, including pay stubs, tax returns, etc.
For more information about working with a bankruptcy attorney, check out Chapter 10 of How to file for Chapter 7 Bankruptcy.