A fine first round purchase is Destroyer, Submarine, Transport and units for the transport. Your priorites are the following:
1. Protect the Atlantic Convoys – you are easily within range of nearly all of them and have no closer targets, making you a far better protector than the British. If your destroyer has survived, you may need it to free convoys immediately. Always free them starting with the highest value within range first, whether it’s yours or British.
2. Invade Africa – Unless German subs have blocked the route to Morocco (in which case you must attack them), sent your two troops aboard your transport to Africa immediately (with your destroyer to support them unless it is required to hunt subs). Do not be afraid of losing the transport to counterattacks; it’s worth it. Ensure you’ve built at least one transport on your first build, and continue doing so for the rest of the game, balanced with producing enough units to carry aboard those you already have, until you’re spending all your money on units.
3. D-Day – When either a) Africa has been conquered by the Allies or b) Germany is already being hard-pressed by the British in Europe, cease the Africa campaign and begin shipping your units to England instead. Attack Denmark, Netherlands or France; all are equally effective.
Your air force should be gathered in England, in order to a) protect against strategic bombing from Berlin, b) sink German fleets, especially transports, and c) conduct bombing raids of your own. Build additional planes when you feel you can afford spending less on transports/units.
Remember the convoys are your priorty; if German subs must still be hunted, suspend or reduce spending on transports/units until you have produced sufficent naval forces to counter them. Do not overspend, since the Germans are not likely to continue producing vast quantities of subs; one destroyer goes a long way. Never build carriers and battleships. Two destroyers are better then a battleship for supporting amphibious landings later.