I agree with Krieghund, let them start with Japan. If you are playing with 3, splitting the Axis is better, since they don’t have to coordinate as much in the opening rounds.
I have to do this quite frequently since (much to my disappointment) fewer people play these days, and so many new boards have come out in the past couple years, that there’s a good chance even veterans from back in the day won’t know the new map or the latest roster. So if you want to play, you have to train opponents.
The best reason to start a new player off with Japan, is that they can observe Russia and Germany, get a feel for how the game phases work, and see how combat works, as well as non-com and placement. Then on Britain’s turn, there is a chance they might see some limited play on defense, before beginning in earnest.
The main goal should be to get them excited and interested in playing, so you don’t want to overload them with info at the outset. You could run a couple sample battles using the battleboard, just so they can see some of the values and get a feel for the way the dice and casualties work.
Play the Allies with no bid, clearly. (It will take too long to explain what a bid is, and just suggesting that the boxed game needs a bid for balance adjustment is a good way to lose new players right away.)
Don’t preset the pieces on the board. Even though it takes a good half hour, it’s good for the new player to place the pieces, and familiarize themselves with the unit types and the map.
If possible (if you have an older board) use the paper money! Removing the paper money from this game was just the stupidest decision ever from the perspective of teaching new players. At least if they have the bills in hand, then there is less mental math and numbers crunching going on, and it is simpler for them to plan their purchases and track their overall progress.
Prebag, or separate the units for Japan into unit types. For example, one ziplock bag of all ground units, and a second ziplock bag for sea/air units. This will save more time than you think, as new players don’t have to spend precious minutes each round digging around for their units.
Give good advice and explain the available options, but don’t go too far with it. You can guide them away from really foolish attacks or purchases, but it’s best to let them learn how to play without too much direction.
Don’t expect to be able to finish the game in a night. Even the stripped down 42 sec ed is probably a two session game. Better to play the opening rounds and let them develop a feel for the board.
Just like in chess, the endgame advantage goes to the player who holds the center of the board. I think you have to explain this up front, otherwise the new player may not develop an appreciation for how to actually win an A&A game.
Encourage world war 2 banter, and glory in the plastic pieces. Getting excited to play with little plastic tanks and fighters is the best way to hook a new player. Don’t judge their strategy too much, just respond to their crazy moves in the way that seems best to you and let the dice roll.
Hopefully they stick around. We need more people to play this board.