Deregulate parking.<p>Right now nearly all municipalities have laws that require a certain minimum amount of parking per square foot of building floor area, with the amount varying by use.<p>This has three perverse effects:<p>1. Buildings cost more (surface parking requires extra land, underground parking is insanely expensive), so fewer people can afford to live close to employment centers, amenities, and transit stations. 
2. It encourages the ownership and use of cars. If you've already paid for parking in the cost of real estate and the price of crap from the mall, you might as well use it.
3. Unless the parking is underground, everything is more spread out, so fewer trips are practical on foot or by bike.