Never buy a J1 IC because, even if the Allies don’t go KJF, on J1 you can’t really tell in which territory it will be most useful. Usually it’s FIC, but not always.
For KJF:
If the UK consolidates in sz30, go after sz52 in force. The UK force can’t get any bigger and the US will make up the bulk of the Allied Pacific force so don’t give them a head start. Don’t needlessly sacrifice Japanese navy so go after sz52 in force always, anyway. Unless Russia stacks in Bury. Then it becomes conditional on board position to determine what’s the right move.
NEVER sacrifice your bomber and always keep it in Bury. From there it can threaten every sea zone surrounding your islands and still reach most of the tradable Asian territories.
Fighters not on carriers should also be based on the coast (FIC, Kwang, Bury). They can cover your land forces and it allows you to use 4 fighters per CV. 2 land based fighters can attack a sea zone 4 moves away and land on the CV while the 2 CV based fighters can land on an available island within range.
Subs are Japan’s best friend. Build as many as you need to keep the edge over the US fleet if it moves out of sz55. Don’t spend the money on a 3rd CV unless the UK/US combined fleet puts you seriously behind in firepower and you already have 8 fighters to max out the CV capacity you start with.
Minus ships on TP and newly built navy protection duty, base your entire fleet out of sz50 unless a juicy target presents itself. Keep your naval influence projected as far out as possible for as long as possible. Don’t give the Allied shipping any extra freedom of movement.
Clean ALL of the infantry off the islands as soon as possible if you can do it. Even the hard to protect outlying ones. When the Allies finally land on them, they will be bringing massive firepower so the infantry left behind will be a lot less useful than if they were evacuated to Asia.
And, finally, don’t build an IC unless Japan is making over 40 IPC’s. With most of your income going into high priced aircraft and navy, you’ll have a hard time maxing out Japan’s production since you’ll most likely also be producing a few armor for offense, as well, because your land based fighters may be tied to the coastal territories.
Japan can go a long way in keeping the Allied fleet out of their backyard. In the case of KJF, Africa becomes the key. If the US makes a token effort to keep Africa out of German hands, the Japanese will be able to build less navy and more ground units. If the US goes full bore at Japan, Germany gets Africa for a song and, as long as they can keep the UK and Russian ground forces separated, they should be able to force Russia from turning an offensive eye toward Asia.