An easy way to add broad diversification is to purchase shares of a diversified ETF with a low expense ratio, like SPDR S&P 500 ETF Trust (NYSEMKT: SPY) or Vanguard Total Stock Market Index Fund ETF (NYSEMKT: VTI). Investing well for retirement requires certain knowledge and a clear mindset that you can rely on to successfully allocate $1 million and watch it increase over the long-term. Include a hearty helping of steady growth With $1 million to invest, it's not enough to preserve your funds; you need them to steadily grow to outpace inflation and beyond.