Begin by checking the "classification" on your valuation notice to make sure the use of your property is correct (ex: RU or FR for residential, CU or CR for commercial, AR for agriculture ect.) Next, compare the current and previous year's values. Does the appraised value appear to be close to the price you would consider reasonable if you were to sell your property? If so, the appraiser has done the job the state requires.
You should also consider whether you have made any changes to the property. Have there been any improvements that could increase the value of your property if you were to sell it? Are there any major structural problems that might not be easily seen from the exterior? Remember, however, general maintenance usually does not affect value.