Theres no perfect way to diversify, but modern portfolio theory suggests holding index mutual funds and etfs is enough.
There are many schools of thought as to the percentage of your investments between bonds and stocks, the old 60/40 rule doesnt apply anymore.
In general, own some stocks, bonds, government monds, mutual funds, cash, etc.
As far as sectors, don’t put all your money in one spot. have some tech, retail, financial, tourism, manufacturing, etc.
It is impossible to completely diversify your portfolio. To do this you would need to hold a stake in literally everything, both traded and non-traded. The best we can do is to hold many indexed funds, across multiple asset classes and geographical regions.
Depending on the investors age should be diversified according to risk as someone in their 20s can take on more risk than a person in their 50s and the move from stocks, to more secure bonds and mutual funds as the investors age to minimize compounding losses and continue to contribute to compound investing over time.