I used to be a stock broker. But right now I am not your stock broker. This is not advice.

Great fundamental wisdom is that you can't (consistently) time the market but you should try to Buy Low, Sell High. That said, we experience a massive COVID crash. It's a great time to buy, but we don't know how long it will last or whether it will be long recession afterwards.

Index investing through ETFs is a great way to get diversity in a single financial instrument such as the S&P (large companies), NASDAQ (tech), or the Russell (small companies.) The NASDAQ has largely recovered but the Russell still has a long way to go back to February prices.

I have an old friend whose parents sold their home recently and gave him a sum. He's putting in 10% per month for the next 10 months, all in the S&P.