Most people want to buy a house that they can be proud of. They want their friends and family to praise their good taste. The fastest way to sell anything is to give people what they want. So, if buyers want curb appeal, here's where you start.
One of the easiest things is basic yard clean-up. Mow the lawn, rake the leaves and pull the weeds. In general, make everything neat. Then look at your mature plants from a fresh point of view. Do they block the view of the house from the street? Have they outgrown their space? Is the shape really right for their location? With this new point of view, give the front yard bushes crisp, clean lines. Cut back plants that have expanded beyond their allocated area. But be careful not to trim back so much that they are woody instead of green. If there are any tree limbs that get close to the building, cut them back. A clearance of 18" or so is adequate.
Repaint your front door an outstanding color. That doesn't necessarily mean a bright color. My favorite colors are light in tone. A front door that is white shows up from the street better that a dark one. If your door is a wood finish, make sure that it is not cracking or peeling. Re-finish if need be.
If you have one of the black wrought iron security doors and you live in a low crime neighborhood, consider removing it. Fill the screw holes and repaint the trim. Security doors cause buyers to questions the safety of the area. You want them in love with your house, not afraid.
New house numbers can make a big impact. In a metal that matches other exterior details, they act like jewelry on the front of the house. Just make sure that you install them straight.
Add simple white blinds/shades to the windows in the front of the house. This gives the house continuity. You have all seen the house with different brightly colored blinds in each window. It might work with the interiors but it creates a mish-mash from the street.
Now that we have the exterior neat and fresh, look to see if it is boring. If you can't tell, ask a friend or neighbor for their honest opinion. You may need to do one simple thing or a combo of things to give the house pizzazz. While there are many, many projects that will provide that sparkle, most folks don't know what to do first. In a slow market, a house without sparkle will not attract the attention it needs to sell. Curb appeal creates that volume of interest.
When have you done enough? How do you know the house has curb appeal? Go outside and look at your house from the street. If you say to yourself "It looks so good, do we really want to sell?". Then you have curb appeal.