let's be clear about this: I would never smuggle and I don't want you to do it. These are just stories of a good friend of mine. He uses the following tricks:

1) the wear-and-tear-ploy: you only have to declare the "fair retail value", which should not be higher at which a secondhand store could sell the item (50% off).
2) The per-person-spread: sometimes, when travelling with his family, my friend will pass immigration separately (with an immigration form for each family-member) and then pass customs also separately, letting the familiy members carry "problematic" items in small bags - he follows with the big (unproblematic) bags seperately.
3) the foreign-receipt fraud: when my friend buys in foreign countries the shopkeepers are happy to give him a receipt for a lower amount.
4) The domestic receipt fraud: my friend always has receipts from shopping at home to "prove" customs that he bought the item already before leaving home.
5) the domestic label scam: my friend takes labels from his home-clothing and sews them into his foreign clothing purchases.
6) the previous trip story: hopefully he can prove it with his passport and he may have produced the shop-keeper to predate the receipt accordingly
7) the sloppy list: my friend will make an almost illegible list of foreign purchases including all items in one column but leaving off one of the (higher) prices in the other column. At the bottom of the prices-colum he puts the (wrong) total. A custom officer searching his bag will find all items listed, but may miss that not every item has a price. If he does, he'll probably think it's an understandable mistake.