Put yourself in a buyer's shoes and walk through each room of your house, and evaluate every area of your home, inside and out. Be honest with yourself. If you were looking to buy in your neighborhood, what would you think about your own house?
Make a list of items that need to be repaired or replaced, and things you can do to make your home more appealing.
For example, start in the entryway and make a list:
You get the idea. Go through your entire house and list everything that should be done. Then just get started, one item at a time, until you're done.
Be sure to pack away all those knick-knacks and family photos as well as repaint all areas that are not 'neutral' in color. De-personalizing your house is important.
Your agent can also be a great help with this process. Agents know what needs to be done and what buyers are looking for. If you're not sure what should be done to get ready to sell, get your agent involved early in the process for their expert advice.