One the best steps you can take is to educate yourself on the laws of your state. There are several sites that can help you with this, divorcesource is one of the largest divorce sites. Equality in Marriage Institute will also give you some great direction. Now back to how do you start writing down what you have/ want.
Start with what you co own/owe, for example: car, apartment, house, land, boat, loans, credit cards, gas credit cards, store credit cards, memberships to health clubs or shopping clubs, etc. List, as best you can, the value of each, how much is left to pay on any of them, how they were paid for (you paid form a savings account, he used his tax refund, you split the cost). What legal papers are your names on?- lease, loan, deed? Now you can move on to smaller stuff- what around your residence is "yours" (meaning you bought it or use it more?) what do you share equally- ie tv, stereo, living room furniture?
What accounts to share? Do you have any money that only you have access to? You should have copies of recent bank statement for you and your spouse. Any stock investments?
Once you have idea of what your laws are in your state and a list of what you have together, with notes as to what you want, you can then feel confident when interviewing lawyers.
Some other must read sites belong to The American Academy of Matrimonial Lawyers and Womansdivorce.