This is a great question and one that is worth $10's of thousands. It all starts here, when the buyers pull up to the house. Many are already sold before they even go inside because you can always remodel to your liking.
Besides fresh paint and flowers, maybe add some trim around the windows, two tone paint, clean windows, nice walk way, flowers on the porch, nice front door. If the porch needs painting or the steps, don't try to save money.
Stag the outside just like you would the inside.