While Kill Japan First (KJF) is not a commonly executed strategy, it still has been known to befuddle folks who have never encountered it.  The following is derived from a discussion on how to defeat a common version of the KJF strategy.  In this scenario, UK has a factory in India, US is likely to place one in Sinkiang, and to use their bomber against any unguarded trannies in SZ60, landing in Buryatia. 

In Japan 1:

Build:
1 AC, 1 TRN, 2 INF

Combat:

• Take China.  Use Kwang INF, 1 INF from FIC, 1 INF from Manch, 2 FIGS from Asia.
• Leave 1 INF in FIC to prevent a UK blitz, and 1 INF in Manch to prevent a Russia blitz.
• Use 1 FIG from East Indies AC to take out UK tranny/sub off New Guinea or Solomons, fig to land in Pearl on Caroline AC
• Attack Pearl with Caroline fleet, Japan BB, Bomber.  You have a 99% chance of winning, 38% with all of your Japan forces, 37% of the time you only lose the destroyer.
• Attack UK ship(s) off Kwang with 1 BB, 1 AC, 2 FIG (one from AC, one from Japan)

Non-Combat and Placement:
Transport 1 ARM and 1 INF from Japan to Manch
Land FIC FIG in Manch
Land Manch FIG on new AC in SZ61
Land Japan FIG on new AC
Land East Indies FIG that fought at Kwang on that AC (SZ59)
Land New Guinea/Solomon FIG on Pearl AC (SZ52) as well as Pearl FIG
Place new TRN in SZ61

Now, I may have missed 1 or 2 small items, but here is how Japan now stacks up:
THREE Carrier task forces:
1 AC, 1 BB, 1 FIG in SZ59
1 AC, 2 FIG, 1 BB (and maybe 1 DST) in SZ52
1 AC, 2 FIG, 2 TRN in SZ61

Land Forces:
3-4 INF in China
1 INF in FIC
2 INF, 1 ARM, 1 FIG in Manch
5 INF, 1 ART in Japan

It is not pretty, it is not glamorous.  But with that much Naval power in the Pacific, the US is NOT going to be able to assist in a KJF except for that Sinkiang factory (2 units per round).  UK is also lacking a navy in the Pacific and will lose the sub off New Guinea and the tranny near India very quickly.

J2, Japan starts their tranny build-up and also takes Bury with an amphib, knocking out USA bomber base, and catching that US bomber on the ground as well if it flew to Bury.

Japan WILL be slowed in J1 and J2 in Asia.  But their trannies are now 100% secure, and the Allies now have to come after Japan in coastal territories where Japan's BB's and naval air power are going to wreak havoc on the Allies with Japan's counter-attacks.  The first example of this will be a counter attack in FIC using multiple FIGs and a BB shot in either J2 or J3.

In J3, Japan will be able to land as many forces in Asia as UK and US can build in both Turn 2 AND turn 3.  Starting in J4, Japan will be landing forces in Asia at at least twice the numbers that UK/US can build them.

Meanwhile, USSR will not be sending forces to help because, with the drain of UK resources to build and support an India factory, they are nearly alone facing Germany (not a good idea).  And, without pulling forces out of India to reinforce Egypt, and with the Germany Med Fleet still in existence, Africa IPC's are going to tilt toward Germany for a few rounds, further diminishing UK's ability to both support the India IC and the assault on Germany.

To kill the KJF:
Establish naval dominance
Establish transport capacity
Attack Allies in coastal areas with large scale amphibs supported by your superior navy.