The most obvious way to reduce the size of an estate is to spend the money. Although this is a good idea in theory, in practice it does not work. People who accumulate wealth are not prone to change their lifestyles and priorities.
Savers continue to save and accumulate.
Investors continue to invest. Spenders continue to spend If spending won't work to reduce the size of the estate, then the obvious answer is to give away the assets. Gifting to the people who would inherit anyway is a wealth shift that reduces the need for expensive, sophisticated methods. Gifts in excess of the annual exclusions are included on the estate tax return at the value on the date of the gift. So these taxable gifts only remove future appreciation from the donor's estate.