Record serial numbers of small appliances and other theft-prone items. Keep receipts along with the description of the item. If doing an audio or video inventory, start in one corner of the room and work your way around until you cover the whole room. Don't forget to inventory closets and the attic and basement. A detailed record of antiques, jewelry, silver, sporting goods, major appliances, and collector's items is very important.
Appraisals are also important.
How often you need to update it will depend on when you make new purchases.