The outside of your home is the first battle. When your home goes on the market, it's listed everywhere right away. (Or should be, anyways) 2/3rd of the folks who could be interested in your home will only see the outside. It hurts, but let's be frank here: appearances are what matters. If the outside looks shoddy, they might not even bother calling their real estate agent to ask for a tour. Keep your lawn mowed regularly, and looking at least a little green, and if it's spring or summer, splurge on a few cheap annuals to fill any flower beds and give it some life. This goes for the front AND the back, especially for photos online. Things don't have to be perfect, but for less than $20 you can make your home look much more inviting AND maybe get a better offer.
Make your home smell inviting. What? You don't think your home smells? Think again. If you rarely open the windows in your home, you might have a musty smell that you're immune from smelling. As a pet owner, I'm well aware that they don't exactly help the smells either. If you can, leave your home for 24 hours, and then come back - you'll probably notice the smell now! So how do you get rid of it? Well, first of all - avoid the temptation of commercial air fresheners. Not only might your prospective buyer hate the smell of lavender or cinnamon, it also screams that you're trying to cover something up. Instead, fight back by letting your windows stay open to create a breeze through your home and whip that smell outside. Next step: try baking something like cookies just before they arrive. Not only is the sweet treat sometimes a welcome to the buyer, it also makes your home smell more inviting and help the buyer imagine what it would be like to bake in your kitchen. (No need to make from scratch: if time/cooking skills don't allow for it, just pick up a refrigerated package of cookie dough and make just a few as needed!)
Make sure the trash has been taken out, the laundry is put away, and the prospective buyer doesn't have to step over a hazmat of toys. You don't need to wipe away all evidence of living there, but folks don't want to end up with a trip to the ER after tripping over a Tonka truck or see the clutter everywhere.
Clean your windows. I know, this is one of my most hated tasks around the home, but you want as much sunlight to show in the rooms as possible. (Unless, your prospective buyer is a vampire. ha!) Do your best to get those windows streak free and sparkly, especially if they are older windows.
Speaking of light, change the light bulbs. Pick a stronger wattage, or a different style of light bulbs to show how much light there can be in a room. At the very least, make sure your light bulbs - and light fixtures - are dust and cobweb free.
Above all, resist the urge to make your home look sterile and staged if you're still living in it - buyers can see right through it.