Set Banking Regulations - large capital ratios - that discourage super large banks. If large banks had large required reserves (high capital ratios) the country would not have had to worry about the banks failing. Banks should not be involved with derivatives and any other very risky type investments. Immediately increase capital ratios for risky instruments.
Capital ratios for mortgage instruments should be directly related to the down payment amounts.
The new rules could be phased in over a few years (3 to 5 years).
Try harder to go after the banks to proscecute for any wrongdoings.