Well, there's a few things to consider. Is the goal defeat of Germany and the Soviet Union both? What time frame is being considered? Is this a coordinated effort on part of the Western Allies?
If we're looking at a "Germany just does a bit better" timeline, then there's a few things that would significantly increase duration of the war, and overall losses.
First of all, Leningrad must fall. This significantly hampered the progress and overall situation of Army Group North.
Second, when it's clear Stalingrad will not be encircled in the initial offensive, pause for reorganization and preparations for another offensive with the sole aim of encircling the city should be taken. Regardless of the outcome, it's crucial that the Germans do not enter Stalingrad directly, and that 6th Army and accompanying forces not become total losses.
Assuming an improved general situation for Army Group South, Kharkov is perhaps replaced by Kursk itself, shortening the line, and forgoing a major strategic offensive on the Eastern Front.
Next, Army Group Center must not collapse, no matter what. It may be defeated, it may be pushed back, but it must. not. collapse.
All put together, this may extend the war into 1946, assuming the Allies do not land in France in 1944. Greece and then the Balkans would be good alternatives.
D-day in 45, and procede as OTL.
From the Allied end, all efforts should be made to rebuild recaptured infrastructure and production centers. European troops will be needed if a death blow is not delivered quickly. German equipment would be a viable choice for equipping French, Belgian, Dutch, and Yugoslavian troops.
Using initial Allied forces, strikes must be made Northwest from Allied Holdings in the Balkans and Romania, and Northeast from the Elbe, aimed at the Greifswald area. Operational goals will be encirclment and destruction of as many Soviet Units as possible, creation of a salient into Allied lines around the Berlin area, clearing the Soviets from the North German plain, and securing their Northern flank against the Baltic coast.
Ideally, sizable Soviet formations have been trapped in a pocket in Northern Germany, important allied lines have been secured against counterattack in the South by seizing of the mountainous regions of centeral Europe and hopefully encirclment of additional Soviet troops in the Southern offensive.
From here, Eastern Germany and Western Poland can be cleared by simulations thrusts from the South out of Czechoslovakia and in the North from Greifswald. Soviet positions must be abandoned or face encirclment and annihilation.
If all goes reasonably well, significant Soviet formations have been destroyed, and their overall situation has been greatly compromised. Capitalizing on their extended supply train, remaining Soviet armies can be operationally immobilized as the German army was in 44 and 45.
After Poland is liberated, perhaps the Soviets accept peace on terms of antebellum borders. Or maybe not. In either case, as soon as is possible, extensive nuclear strikes must be carried out against Leningrad, Stalingrad, Moscow, Kursk, and if possible Tankograd.
Bomb everything on the Pacific Coast and in the Baltic and Black Sea with carrier aircraft, and shell the absolute hell out of Sebastopol.
Show the Soviets just how incapable of waging war against the Western Allies they really are.