In the Pacific, I normally keep a continuous flow of destroyers, subs, and sometimes battleships or loaded carriers from Western US, Hawaii, and Australia. This keeps Japan and the DEI threatened, protects Hawaii and keeps ANZAC transports covered. Subs are very usefull here because they force Japan to keep buying destroyers. The less money Japan can put into to land units and transports the better for the allies. It’s also usually worth it to suicide your units to kill Japanese capital ships because they generally can’t afford to replace them. At least not at the rate that the US can. If you start eliminating carriers and battleships you’ll see Japan retreat from the DEI and India every time.
As far as Europe is concerned, it all depends on how the fight in Africa and Russia is going. You can land units in Africa straight from the Eastern US in order to poke Italy a little bit. I personally like to have a nice little “transport bridge” from Eastern US, Gibraltor, and SZ 110. A loaded carrier, maybe a battleship, and a couple of destroyers combined with the UK fleet should be enough to keep the German fleet at bay. With this setup you can hit Normandy every turn to harass Germany and help the Soviet Union out. Or you can go for the Med. and hit Italy pretty hard. It all depends on which axis power needs the most attention at the time.