Whether you're using "My Belongings" Online Inventory System or some other method of recording your home or small business inventory, there are several general techniques you can use that will save you time and effort:

Record only the larger, or more expensive items - Everyone will have a different threshold, but as a general rule If it's less than $100, don't spend any time on it.

A picture is worth a thousand words - While text information, such as serial numbers are important, pictures of the item are priceless.

Perform your inventory on a room-by-room basis - Methodically go to each room and record the items in that room.

Perform a two pass sweep - On the first pass, get just the initial, general information about items.  Then print out the reports (by location) and use this on the second pass to fill in missing information and details as needed.

 
No matter how you do it or what method you use, the important point is that you document  your belongings.  This is almost always the first thing anyone who's been through a situation where their belongings were missing or destroyed will tell you.