Are you Lloyd George? That's what he said
Working Class Hero said:
Increase the battleship blockade on Germany,
Wouldn't do much good. The neutral states were only allowed to import enough for their own needs. No doubt a little got through, but not enough to make much odds.
knock Turkey and Austria Hungary out of the war earlier (this wouldnt be difficult, Austria in particular was an anachronistic throwback to the nineteenth century)
They tried. That's how and why Italy came into the war, and why persistent attempts were made to get Greece and other Central European powers involved. Didn't do much good.
and try even harder to starve Germany out of the war.
How? The blockade was about as effective as it could be.
Towards the end, subsidise German or Swiss Communists to cause even more trouble amongst the German workers (there was an attempted revolution in 1919).
How far was the revolution a result of defeat? It didn't happen- for all their fears- in Britain or France. Certainly the High Seas Fleet mutinied when their commanders tried to take them out for one desperate effort, but the army remained solid almost to the end.
Make a focused effort to destroy the war effort from the inside, because even in 1918 the German army was a viable fighting machine, at least defensively.
It was defeated militarily after March. They were retreating steadily and sometimes were suffering complete local defeats. The armistice came because the German army would soon be broken.
And like alot of other people have said, make use of new technology an tactics like Storm Troopers and gas.
New technology, to be really effective, would have had to be introduced before the war to give time to make and use it properly. There are some surprising things- that no-one introduced the smg, even though it took months to properly train a rifleman, that no-one looked at the use of aircraft as offensive weapons before the war, but given what the armies had in 1914, and the first months of war, what followed was predictable.
Poison gas didn't make a breakthrough. Even stormtroopers only succeeded the once and only temporarily- with the fortuitous aid of fog and because- thanks to LG- they were attacking an overextended and undermanned army.