The very first thing that could avoid it is avoiding WWI. The way governments financed WWI broke the gold standard, which made the global economy incredibly unstable.
If WWI is a necessity, there are certain things that 'can' be done to avoid the Great Depression, but you're going to have several decades of financial and economic instability regardless. While it's technical possible to avoid THAT outcome, it borders on ASB because the reforms necessary to achieve just couldn't be made to happen in a reasonable time period (10-20 years).
So, let's work backwards. Starting from 1930 (when the Great Depression went from a nasty deflationary recession like happened in '20-'21 to being the actual GREAT Depression), what could be changed?
1. Do anything to stop the Smoot-Hawley Tariff. Smoot-Hawley, and the retaliatory tariffs put on American goods by other countries, are what set off the bank failures that would cause wave after wave of runs over the next few years. Pretty much, once Smoot-Hawley passes
nothing can stop the world from spiraling into something nasty. It doesn't
have to be a ten year depression like happened in the US, but it's going to be something.
2. Make sure Hoover stops thinking so highly of himself. All his moralsuation and voluntary interventions in the early years of his administration made the economy weaker than it would otherwise have been. Most importantly, the 'high wage' policy he convinced several major corporations to follow kept the economy in disequilibrium throughout 1930, even if recovery started rather quickly.
3. Get the right people in charge in the world's central banks. Britain's abstinent insistence that she return to the gold standard at parity with its pre-war pound was stupid and contributed to that entire decade of economic weakness. France's gold hoarding was terrible, and more than anything but Smoot-Hawley and the Federal Reserve's own gold hoarding caused the 'Great Contraction' (the fall in the US money supply by 33% between 1929 and 1933). Things actually didn't work
that badly in the 1920's when the central bankers of the world were working together.
4. To get a bit more specific, there are several policy changes that ultimately did more harm than good. Again, working backwards:
4a. The Federal Reserve blew and then popped a major asset bubble by alternately pursuing overly inflationary and then overly contractionary policies between 1927 and 1929.
4b. Both the Federal Reserve and the Bank of France were downright stupid when it came to their gold reserves. By 1931, I think, between the US and France you had
70% of the world's monetary gold reserves, but less than 40% of total output.
4c. The aforementioned thing with Britain insisting on returning the Pound to its pre-war gold peg. Basically, after inflating her money supply during WWI, Britain had two choices: 1. Set the peg at its new parity or 2. Let her economy deflate enough to repeg at the old value. But she wanted her cake and to eat it, so she wanted to repeg at the old value without deflating her economy. The Federal Reserve was very accommodating, but all this ultimately did was cause the entire international financial system to continuously de-stabilize.
5. Keep the immediate post-war system of floating exchange rates. The way the world works, you can really only ever have a central banking system or a gold standard. The metaphor works like, "Two men ride a horse. ONE of them has to be in front". Since you no longer had the US without a central bank, the gold standard wasn't going to work like it had prior to the Great War. The floating exchange rate system that ran from 1919 to 1922 allowed for more freedom for the world's central banks to pursue independent monetary policies without introducing macro-economic instability like happening later on in the 20's (where the gold peg transmits instability in one economy to all the others).
6. Dramatically lower Germany's reparation burden following Versailles. It won't get rid of all your problems, but it takes one factor of instability away.
OOOOR, my favorite, go all the way back to 1844 and prevent Parliament turning the Bank of England into a proper, modern central bank in the first place, retaining a system that more resembles free banking. Viola, economic instability problems solved