This isn't really history, and I doubt any Best Answer will actually be the best answer since it's all down to opinion and point of view, but here goes. Simple numbered lists so it's easier to understand. 1) Having the Japanese attack the USSR as well, and persuading them not to attack the USA. That would have still left Britain as the only opposing power in the West. 2) Changing strategies. Hitler may have been a genius (I don't know), but he should have known when to change from the Blitzkrieg tactics. Also, he should have focused on the oil fields and strategically important locations. And, most importantly, known when to give up and move on (Stalingrad, Leningrad). 3) I would say no Holocaust, and treating the Soviets more fairly, but that would go against the very core of Nazi beliefs, wouldn't it? So I'll leave that out. 4) Researching into opposing forces in the USSR, and helping these forces create distractions within the country. Guerilla warfare can be extremely successful. And, it's much cheaper than launching a full scale invasion. If you have the right tactics, good organisational and leading skills, then this could have proven fatal. 5) Coordinating with Japan. If Germany did get Japan to declare war on the USSR, then what they could have done, is coordinate their attacks. This would divide the Red Army, much like what happened to Germany with the Allies and the USSR. 6) Focused on Moscow. Once Moscow was taken, panic would automatically ensue. Plus, with the guerilla warfare tactics, Hitler could increase support among the ordinary peasants, who were, most likely, sick of, as I like to call it, pseudo-Communism. This could have led to a case similar as in Vietnam. 7) As far as Stalingrad is concerned, this was indeed a turning point in the war. Hitler was indeed childish here. See, the city's called STALINgrad. Stalin was the leader of the USSR. Similar case in LENINgrad. He wanted to have some self satisfaction, and like, show his might to the Soviet leaders. 8) He should have taken some initiative towards the Bolsheviks in Russia. He thought the ordinary people would automatically come out in support of the Nazis, however, if he went and did a Holocaust, as far as the Russians could see it, it was a choice between the greater evil. And they believed Germany to be the greater evil. 9) China, which was in a state of anarchy at the moment could have also helped. See, if Japan signed a ceasefire with China (ROC), then much of its resources could have been saved. The way I see it, what they could have done is propped up the Nationalists, and poured money into their war effort. This way, not only would they have massive influence in China, but the USA would also approve of them (the USA was also helping the Nationalists in China). 10) Russia can be conquered. There is no force on Earth that cannot be conquered. Russia is no exception. Russia has been conquered in the past. The Mongols did it. And if they could, why can't anyone else?