Don't just limit yourself to the stock exchange. Majority of the time, the way market algos operate, correlations turn to 1 during sell-offs!
Also, do not limit yourself to just one way of doing things. Think and look outside of the box at both equity form & in debt form.
Diversification only starts with stocks & bonds. While it's enough for some, why settle there?
While not create a properly diversified & thoroughly risk balanced portfolio?