Invest in a crypto market situation accordingly. There should be a framework for him to invest in which time to invest. And at what time to sell.
I think few people can share a profitable strategy , I think in a falling market can earn only experienced people, and in the bull market you can buy almost any coin and keep six months and you will bring good money
What you earn in falling market? Market, every market needs to have two sides, buyer and seller, money and product, or money and money, when cryptomarket is rising you are dumping coins for money, when cryptomarket is going down you are buying coins, so you are dumping the money, but you have more coins. What you earn depends from your strategy, if you aim just for profit in fiat than you probably lose fiat over time, cause you need to be aware of both sides. My strategy is long term, for now I`m losing money, but I`m getting more coins, I think it will pay out in future, its risky but its my strategy.