First of all, you need to know what contents you’re insuring. If you were to turn your house upside down, any item which falls out would be considered contents. Carpets and curtains would also be considered contents – however, any fitted kitchens or bathrooms would NOT be considered contents.
When you estimate the replacement cost for your items you should calculate the cost for your insurer to replace them and not what you paid for them. The total of this is the amount you should insure your contents for.