Tidy up, put things away, make sure all stairways, hallways, doorways etc are clear. Kitchens and bathrooms should be spotless - including the sinks.
Most people are decent, courteous and honest but it's wise to store valuables like jewellery, cameras and other small valuables in a secure place.
This one is pretty self explanatory. Buying a home is an emotional thing... just baked cookies, freshly brewed coffee etc are generally positive, "homey" fragrances that might help people to connect to your home in a positive way whereas strong seafood smells may not have the same effect. If you know someone is coming plan appropriately.
Try not to be present during showings. You want people to feel relaxed and comfortable to look around and comment freely and that's not possible if you're there. Don't worry, if they have questions your REALTOR® will get them answers later.