As far as upgrades goes, simply put, it is recommended to do every available upgrade before you call in your first airstrike. The list of the air upgrades that follows is NOT to help you choose which upgrades to get, but to educate you on the inherent advantages/disadvantages of each country.
 
    ^{Click the top of the columns to sort the table}
 

What follows is the "unofficial" regiment ranks for Axis and Allies Airpower. Notice that the overall strength of airpower parallels the strength of the bombers; as the fighters have little to no effect in normal online play.
 
Click the top of the table columns to sort the table (the default sort for all tables is by country name).
 
 

The airfield is the only building that can be "rotated" in the same manner as bunkers (for example see engineers). Simply hold the click down when unpacking, and rotate the mouse to rotate the airfield; and release. Just be careful it's how you want it, since the airfield is also the only building you can't pack and move.
 
The advantage of rotating the airfield is that your bombers may have an altered "flight path", which in some cases totally bipasses enemy anti-air defenses. You'll have to experiment with this as it produces some strange behavior at times, and largely depends on where you place the airfield and how it's rotated (try it on the edge of the map).

It is important to use hotkeys so that you can deliver multiple airstrikes to a target location in a tightly grouped formation. The quicker you can launch the airstrikes, the more grouped the formation will be; giving your opponents less time to react as well as your planes a better chance of getting through any enemy anti air.
 
What follows below is a basic example of how to hotkey your airfields. Notice that you can hotkey the buildings by selecting them, and hitting CTRL+(0-9) or by right clicking an empty slot on the group control bar. These same method can be used to hotkey any regiment or structure.... For more about hotkeys, see Keyboard Shortcuts.

Once you have "hotkeyed" your airfields it becomes much easier to launch attack... When used in combination with other hotkeys, multiple airstrikes can be ordered in a matter of seconds... for example:

Destroy the Target(s)
Airstrikes are expensive so it makes no sense to use them to simply wound or damage your target(s). Units can heal and buldings can be repaired and fortified. By the time you order your next airstrike(s) enemy anit-air may stand in your way...
 
Versus Buildings
If you are targeting structures make sure to send enough airstrikes to destroy the target. To destroy an enemy Corp HQ, it will take at least 4 fully upgraded USA airstrikes, and possibly more if you use splash bombing or another country.
 
Versus Units
If targeting enemy units, keep in mind to outright "kill" most armored regiments, it will require two airstrikes, which will cost you more than it costs the enemy to replace it; so best to coordinate with an offensive push, special op bomb, or a simultaneous attack on their armor hq's for maximum effect and kills.
 
Target Selection
Target selection will vary largely depending on game situation and personal play-style. Here's our basic recommendations:

1. Corp HQ - Airfields are great as Corp HQ killers, and no enemy Corp HQ is one step closer to victory
2. Airfields - Disable their ability to strike back or target your crucial base structures and regiments
3. Technology Buildings - You've taken out their Corp HQ, now make sure they can only produce crappy regiments
4. Armor HQ's - Weaken the enemy front lines by destroying their armor hq's, ensuring their regiments are unattached
5. Enemy Units - Usually late in the game when all valuable buildings are protected by anti-air defenses

The Bombers and the Bombed
Civilians bore the brunt of many bombing campaigns, enduring the terror and uncertainty of enemy raids. This is the story of two cities - one British and one German - that suffered the full destructive horror wreaked by the bombers.