Clean up, shampoo the carpets, paint, touch up, mow, trim and do all those things that make it look its best.
To ensure the best appraised value of your home, make sure that everything is in good working order. The home should be well maintained. Also, if any homes in your area were sold without the assistance of a realtor, the appraiser may be able to use those as "comps".
Although there is very little that will "change" the value of your house, it is important to give an amazing impression. An appraiser who is looking at a house filled with garbage will not get a warm fuzzy feeling. If you take the time to make sure everything is immaculate and welcoming it will not change the value, but it could sway the value a little in your favor.
Make sure you are there to answer any questions the appraiser may have. If you have done any work on your house since you bought it or refinanced last, make sure you let the appraiser know.
It is important to ensure that your appraiser understands the markets and trends in your specific area. In a county like Los Angeles County, for instance, an appraiser that is familiar with homes in Stockton would not necessarily be up to speed with homes in Beverly Hills. Therefore, it is wise to make sure your appraiser has done recent work in your neighborhood in order to give the most accurate assessment of your home appraisal. This might not come as any surprise to you, but you would be surprised how often an appraiser tries to specialize in multi markets, becoming a “jack of all trades”, so to speak, but a specialist to none but where they personally reside.