I usually buy 1 fighter per round and fly it over to help out the Brits in Egypt against the Italians.  That is usually really good for keeping the Italian navy in check.  The rest I usually spend on inf and art to try and defend Calcutta when the Japs get there or if Japan’s land force is not doing so well, send them up to help the Chinese pound them even further. I also try to land at least 2 inf each on all the DEI islands so Japan has to at least fight to get them.  Depending on what the Jap Navy is doing, I sometimes buy a destroyer or two to use as blockers just to delay Japan’s invasion one extra round.  Sometimes that is all it takes.