# Avoid using low morale fighter units (<50) unless it's robust airplanes vs. unescorted bombers.
# Use traps (heavily defended airfields and radar stations; I kept hundreds of Flak at Katwijk radar and it downed >1,000 fighter bombers, taking the Typhoon units almost entirely out of the equation) against the AI.
# reduce France and Italy defence to minimal early on
# send all crap units to Romania (all the Axis allies)
# have few French airfields heavily defended, but occupied by only one fighter group (not farther north than Paris)
# avoid using airfields in range of Spitfires and P-47C (nothing in Belgium, Netherlands!)
# There's no really good nightfighter. You need to make do with 110 and 88. Their radars will be upgraded slowly, so don't change the aircraft equipment very often.
# The Fw 190A-5 and A-6 are good fighters. Change Bf 109, engine and parts production to 190A-5.
# Change much aircraft, engine and parts production to Ta 152C. It's the solution for all daylight troubles and can arrive as early as April.
# Be reluctant to change large production plants (long conversion time) unless you have no use at all for the output.
# Concentrate your interceptor efforts on one big raid at a time. This tears away its fighter escorts and destroys many damaged bombers that would otherwise escape.
# Use smallish (staff swarms, individual squadrons) and low morale units to destroy stragglers.
# Concentrate heavy AAA at the three big synthetic rubber plants early on.
# Re-equip your allies with old fighters if possible (especially Bf 109G-6).
# Feel free to not waste good pilots in 109s. Limit their units to easy missions (stragglers, for example).
# Do not try to intercept reconnaissance aircraft until you get the Ta 152C (and the few Me 262A-0).
# Either mass half or whole wings on heavily defended airfields or disperse them on normal ones out of range of most enemy fighters.
# Move fighter units if their airfield has come under severe attacks.
# It's possible to launch fighters more than once against a bomber stream if it's penetrating very deeply. Use the reduced-size units preferably against stragglers, though.
# Equip your divisions in Italy with much AAA and lots of balloons during winter. About the same level of equipment for all, and replenish them regularly (front-line divisions first).
# Do not re-equip your 30x fighter wings with other aircraft, in fact, probably don't use them at all. You can turn them into daylight units in spring '44 if they're still equipped with the old aircraft. Their losses in daylight will be horrible prior to that even against unescorted bombers and they react very slowly to commands. Furthermore, they're quite ineffective at night.
# Employ machineguns exclusively on airfields, and only so if all other anti-air equipment has already been distributed.
# Remove valuable anti-air weapons from evacuated factories (I also remove AA from South Italian, Sardinian and Corsican locations).
Problem with Bf 109: It's too fragile. This in combination with its poor firepower means a poor kill ratio, and a poor kill ratio (= high pilot KIA per 1,000 sorties) means that pilots don't accumulate enough experience, average and median experience drops, you get less really good pilots (>75) who are responsible for the vast majority of kills.
This should be your primary concern. Look at the ratio between sorties and KIA.
Fw 190A is not good at high altitude, but it packs a punch and can survive much punishment.
Ta 152C offers a great all-round package and even includes a great range/endurance that allows for an entirely new use of fighter units. You can mass much more groups on one bomber stream and even maintain individual flights on patrol to counter photo reconnaissance.
Bf 110 can be used early on out of range of fighters (with WGr 21 armament), but it should be possible to re-equip these units soon. Use them near Ploesti (Romania) if you still have them in December.