What should Churchill have done differently?

Now that's a good question!

In WW1 he should have abandoned the Dardanelles expedition once it became apparent that the eventual landing was to have all the surprise impact of Christmas.

In WW2 his meddling and seeming determination to re-run the failed Mediterranean strategy of 1915 - this time in Italy - threatened to undermine commanders and leave a hazardously narrow window for the long-awaited "second front", but the associated aborting of a 1943 cross-Channel effort may have made the difference between triumph and disaster.

His greatest political blunder was to have clung to Britain's waning Imperial pretensions instead of launching the country on the road to European integration when the matter came up in 1950. But others showed just as little farsightedness.