Talk Japan out of bombing Pearl Harbor. That would have kept us out of the war for another year at least. Get Japan to invade from Manchuria. Do not declare war on the US. Remember, after Japan attacked the US, Russian was no longer threatened by the Japanese and pulled most of its troops off of the Manchurian border, freeing them to fight the Germans. Could this have happened in reality? I don't know, the Japanese where dead set on having a Pacific empire, and saw our fleet as their biggest threat.
Cut a deal with England, even if you have to lie to do it. Back off of them. Quit bombing them. Say your beef is with Russia.
Keep pumping money into making an A bomb. Then in about 1945 or so drop a nuke on London when they don't expect it. They might have pulled it off if we weren't bombing the heck out of Germany the whole time. A few years latter when your working on the V-4 or V-5 generation of rockets start nuking the heck out of New York and Washington D.C. That same Summer have the Japanese let loose millions and I mean millions of their balloon fire bombs. They didn't work in real life mostly because they where released in a wet year.
I'm with Jim V, treat your "liberated" Russians as friends. Feed them. Lots of Russians didn't exactly like Stalin, seeing how he killed millions of them. Use good old fashioned propaganda.
Avoid city fighting like Stalingrad & Leningrad. I can't recall the name of the city, but there was a northern port city (Novgorod?) that was better defended than Stalingrad with lots more troops there. However the Germans concentrated most of their heavy artilery there. They destroyed the city gradually, with low losses. Stalingrad was taking place at the same time, but without enough heavy stuff they couldn't effectively dislodge the defenders.
Winter time, hole up. Don't try to manuever, pull back to defensible positions. Make them come to you. The Russians are just better with cold.
And start building more Me262s. That way when/if America decides to come a calling you have a more effective way of knocking their heavy bombers out of the sky.
Ok, enough rambling. Can you tell that I've thought about this a little. I'm a big fan of alternative history sci-fi like Harry Turtledove.