Change the password on your email account; better yet, set up a new email account that your spouse doesn't know about.
Frequently, spouses have knowledge of one another's email passwords. In fact, many spouses routinely access the email of their spouse. When you separate, you do not want your spouse accessing or utlizing your email account for any reason. Do not give your spouse the opportunity to access your account and see potentially confidential information (for example, an email from your attorney).
Change the PIN number on your debit cards, credit cards, bank accounts, etc.
Make sure that your spouse does not have the opportunity to access your financial resources. It is not unusual that a spouse headed for divorce removes funds from the accounts in order to control the money -- don't let this happen to you. If your accounts are at the same bank as your spouses, then you may want to consider opening new accounts at a different bank.
Change the beneficiaries in your estate plan and on your life insurance policies.
Chances are that you have named your spouse as the beneficiary on everything that you can possibly name him or her on -- change these. You should consult with your attorney on this point so that he or she can best advise you how to proceed, but don't overlook this very important issue.
Remove your jewelry and other small, but valuable property from the marital residence.
Any small items of personal property that are valuable to you, whether monetarily valuable or of sentimental value, should be safeguarded from your spouse. Although the hope is that divorces can be amicably resolved, they do sometimes turn ugly and you do not want anything to happen to your great-grandmother's wedding ring or the baseball that you caught at the Cubs game.
Stash some cash.
In order to make sure that your spouse does not have the ability to leave you without any financial resources, it is a good idea to have some cash that you can rely on in an emergency. You may want to consider keeping some money in a locked drawer at work, in a locked glove box of your car, or have a friend hold it for you. Although you will have to disclose the money later, you want to be in control of some money.