Don't bother upgrading airbases that aren't going to be protected by flak.
Upgrade all the cities in the Ruhr. (and build new ones). Upgrade/Build up Berlin. Munich. Vienna. That sort of thing.
Park all your short range fighters in the Ruhr. Transfer all the Flak Regiments that are uselessly protecting ports and things in France etc.... to the Ruhr. Use your RR Flak to fill in gaps, but be ready to move it around from turn to turn.
Park your long range fighters in the middle (or around Ploesti if the allies have Foggia and/or Corisica). The fighters around the Ruhr will strip off his drop tanks, leaving the bombers mostly unescorted when they reach the middle targets. They will take fearsome damage.
Don't use your bombers where they can be destroyed on the ground. If you waste them trying to interdict allied supply in Italy, you will lose them. Not worth it. Instead hide them away....save them for a rainy day. When the allies are invading France, use them to destroy airbases in Italy. It will stop him from bombing your southern cities...which are VP's.
Put all aircraft squadrons that aren't single engine German fighters on RESTRICTED. You don't want any pilots going to them. It will also stop them from getting replacement aircraft, but you can fix that later, since you wont be using them.
Put all single engine German fighters on TRAINED PILOTS ONLY. You don't want them to get any poor pilots.
Put the Night Fighters on RESTRICTED. These are a large pool of trained fighter pilots for use later...you don't want to pollute them with poor pilots. Let them train up on Bomber Command.
Make sure all the ZG squadrons have heavy fighters in them. You don't want them flying night fighters.
Poor pilots = operational losses. It also equals free kills for the allies, and used up fuel....for very little effect. Your experienced pilots will get better and better as they kill allied planes. But after a while, the pendulum will start to shift. When the squadrons upgrade from 40 to 68 aircraft, disband all the night fighter squadrons, and put all those trained pilots in your fighter squadrons. You just doubled the size of your defence. Let flak deal with the night bombers.
If the allies notice that you aren't flying any night fighters, you can always switch the ZG squadrons over. A nasty surprise....
Park the air transports near Essen on an airfield away from the city. They have easy access to unlimited supply for flying air transport missions. I usually move around 3000-4000 supply in unescorted day missions to the front line.
Put all the allied fighters (Italian/Rum etc) around Berlin. In the early war when Italy is still around, you can have fun with the Italian airforce and burn it off bombing whatever you want....its free. I parked it on Sardinia to use against invasion. I also used the German Patrol aircraft here until it was destroyed. Just make sure they don't get any pilots.
Turn off all auto training. They will learn more against the allied aircraft then on their own. Turn off all auto Naval patrol for Germans....let the Italians do that until they surrender.
“My logisticians are a humorless lot … they know if my campaign fails, they are the first ones I will slay.” – Alexander the Great