ETFs are a great investment vehicles for investors which enable them to move through all market asset classes. There are several steps for building up your ETF portfolio such as to determine the right allocation, implement your strategy, monitor and assess. Read the whole article on how to build and diversify your ETF portfolio on Investopedia.
Larry Berman on ETF
Not only do you need geographic diversity, but also you need to have diversification of asset classes such as bonds, REITs, utilities, etc.