Approach your coat closet the same way you would your clothes closet. Give away all of the ones that don't fit, flatter or suit your current lifestyle. There are so many local charities that would be more than happy to take them off your hands.
When buying a new one go for classic style and make sure it fits perfectly. Most important-make sure you LOVE it. You want to feel GREAT everytime you put it on (and off and on).