"My spouse and I plan to divorce but haven't started the process. What should we do first?"
If you and your spouse plan to divorce but haven't started yet, my recommendation is that the two of you sit down and talk and see if there's any common ground between you. Can you agree as to who the kids will primarily live with; can you agree as to what the income is; can you agree as to what the assets are; is it possible for one of the parents to keep the house; are you able to sit down and work out a budget for each party, to see whether keeping the house is doable; if you own a business, can you decide who will keep that business?
If you can resolve these sorts of questions and come to a consensus on how you would like to work things out then, when you get to lawyers and into the system, you will have much less to argue about.