EVERYTHING! Dust the top of the refrigerator, lights, ceiling fans - everywhere. Cleaning dust off of your furnace and water heater in your utility room makes a huge difference in the presentation of that area and can make a ten year-old unit look nearly new. Wipe out cupboards and wipe off walls. Make everything shine! Declutter all of your rooms to show off the cleanliness and space.
The personal items in your house are what make it your home, but now your goal is for someone else to envision it as theirs. Keep some personal artifacts around to show what a well-loved home you have, but not too many. You want potential buyers to be able to picture their things, their furniture, their LIVES here. If they are too busy looking at your pictures, knick-knacks, etc, it can distract them from the reality that THEIR things would go perfectly in this home.
If it's broke, fix it. Replace burned-out light bulbs. Touch up scratches in walls. Tighten loose screws or knobs. Remove carpet stains. Replace that old shower curtain. Everyone has little things around the house that they have been meaning to get around to fixing. Now is the time to do it. You learn to live with the little things that might need attention in your house, but a prospective buyer will notice them right away. And those little things affect the impression they have about you home. Try to walk through your house as if you didn't live there. What would you notice? A good place to start is the front door. It is the first close-up impression a buyer will have. If it needs paint or a thorough cleaning; do it. Your agent should be able to give a fresh perspective and help point out the little things that will make a big difference in the eyes of a buyer.
If the inside of your home hasn't been painted in the last ten years, it probably needs it. Keep the colors warm but neutral. If you have painted recently and have used bold colors that suit your personality, it may be fine to leave them. Some buyers are going to paint regardless in order to make the house their own, so it won't matter to them. It is also possible they may love the colors you have chosen. However, if you have several showings and the feedback is that the potential buyers were turned off by the paint colors, you might want to go ahead and change them or offer a paint allowance up front. Remember, opinions vary. It is nothing personal and different people have different tastes when it comes to decorating.
You don't need to have a professional landscaper finely manicure your yard daily, but you do need to keep it properly mown and weeded. A few well-placed flowers and plants can also add a lot of curb appeal and give a great first impression. Keep driveways and patios swept and kept free of debris. A deck in need of staining can be an eyesore to a potential buyer - take an afternoon and give it a good coat. It can make a world of difference.