I don't know enough to turn the tide completely by myself, but if I could I would bring tons of technology from the future, and I would also try to make him his second hand so that I can make sure he doesn't do stupid shit. I'd also make sure there were no concentration camps and to enlist as many soldiers as possible from all groups, not just Germans. Also try to assimiliate the conquered areas ASAP, and if you're feeling really cynical, only put them in forced labour, not death camps.
Make peace with western Europe, make sure Japan doesn't invade USA or do anything retarded. Maybe ally with China if possible instead of Japan.
Make sure Italy doesn't invade Greece, ask Mussolini if you can take control and arm his army because he's fucking retarded.
Create proxy wars in the Middle East, fund rebells against the British Empire (Hitler actually planned this but it never happened), make sure you're on good terms with USA.
Tell him the future of Europe if he loses. If he wins, I will teach him about economics to make sure he doesn't go full Soviet-mode and never trade with other countries because that will just make Germany poor as fuck and eventually turn into Russia in the future (in terms of economics).
Don't invade Poland, ask to ally Poland and UK instead to fight off the gommies.
