Credit cards: Any joint accounts should be paid in full and then closed. If you have an unpaid credit card balance and only shut it down to new charges, either party can reopen the card at a later date, leaving the other person equally responsible for the new debt. Make it a priority to get the balance paid off so you can permanently shut down the account.
Loans: You need to establish who is responsible for any outstanding debts (typically, this is part of a divorce agreement). When that's been decided, the crucial final step is to make sure that the loan agreement and the title are switched to the person who assumes responsibility. For example, if your ex gets the house in the divorce, he is to refinance the mortgage in his name only and switch the title solely to his name. Failure to do so can ruin your credit score if your ex falls behind on payments.
Beneficiary designations: Update the person you have listed as your beneficiary on every investment, retirement, and savings account as well as your insurance policies. No matter what your will or trust says, if your ex is still listed, he could inherit your assets.