Start by researching the different types of ETFs available, such as sector-specific ETFs, commodity ETFs, and international ETFs. Consider your risk tolerance and investment goals when selecting ETFs, and don't be afraid to invest in multiple types. You can also diversify your portfolio by investing in both growth and value ETFs, and by allocating different percentages of your portfolio to each ETF. By diversifying your ETF portfolio, you can ensure your investments are working for you in the best way possible.