Several policy mistakes were made during the 1930s that turned what could have been an ordinary recession into the Great Depression. Let's review just a few of them in the interest of not repeating them.
The Fed won't let the money supply decline
It is true that the Fed let the money supply decline in the 1930s. This is a frequent charge, and it is true. However, why the money supply declined so much is rarely mentioned.
We now have bank deposit insurance
The money supply declined in the 1930s primarily because of massive bank failures. That was before deposit insurance, which we now have, and which has recently been augmented. Bank failures will be rarer now and the Fed has one eye on the money supply while the other is on interest rates.
We are all Keynesians now
Keynes published his General Theory of Money, Interest and Employment in 1936. His central message of sustaining aggregate demand, using government spending if necessary, is now well understood by economists that will be advising policymakers. Presumably, there won't be any tax increases or valiant attempts to balance the budget during a sharp downturn. Keynesian economics has its shortcomings during good or normal times, but it is still valuable as a depression fighter, which was why it was conceived.
Stay away from beggar-thy-neighbor policies
Trying to stimulate your economy through exports at the expense of your trading partners is not a zero sum game; it's a negative sum game. Competitive currency depreciations help no one and hurt everyone. The Smoot-Hawley tariff has to go down in history as the biggest economic mistake of all time.
An artificially strong dollar is not our friend and an artificially weak dollar is not friendly. Hands off everybody!
Competitive devaluation hasn't begun yet, I don't think. However, the dollar has appreciated considerably recently, which hurts our net exports and aggregate demand, and helps those of our trading partners whose currencies have depreciated. We seem proud that the dollar has again benefited from a flight to safety, but we don't really need to be the buyers for all the sellers in the world. We should keep hands off exchange rates and insist that our trading partners do the same. What has happened so far is, in my opinion, a market phenomenon without sinister implications.
Also, watch out for competitive guarantees
Ironically, we have seen something new, at least for me. That is that one country's guarantees of its bank deposits have attracted deposits from neighbor countries without such guarantees. That has led to follow the leader reactions and a better understanding of the unintended consequences of well-meaning policies.