Preparation for an appraisal isn't really all that demanding. The primary thing is to make sure the house is able to be viewed in its entirety by the appraiser. If there are boxes or items blocking their walking ability, just shove them out of the way.
Most people get worried if their laundry isn't done, or their beds aren't made. I promise appraisers have seen it all and that is not a concern of ours.
However what you do need to be aware of is if there are any broken windows, handrails, some exterior touch ups that need to be done. That does effect the condition of the house.
So just make sure that the entire house is able to be inspected, deferred maintenance issues are tended to, and best tip is don't follow the appraiser around while they are working. When you are at your desk working, you don't have someone talking to you constantly, do you? So just think of your house as the appraiser's office. They are professionals, and have a system to getting through their inspection, but your best bet is to not interrupt them or throw them off their game.
Another item you could have prepared is a print out (or send an email to your appraiser) of the water system or company your home is associated with, same for electrical, are you on septic, is your heater gas/propane or electric, and if you live in an HOA who is in control of the HOA and who maintains your neighborhood amenities. Also, if you ahve a copy of your metes and bonds of the property or a plat, a copy would be great to give to the appraiser, or just out on the counter so they can scan it for their work file.