For the early US turns a lot is going to depend on your overall Allied strategy and what the UK is doing. To start the game the US doesn't have much to do in terms of combat but you want to make sure you buy the right units and start to move your forces into a more useful position.

Since there probably won't be much to do in combat and you will spend most of your turn backing up the other Allies, I'll go into a little more detail about some possible purchases.

1 - Multiple trns + gound units -
Here you are intent on getting maximum troops to Afr, then shifting to Europe. Some weaknesses are you might be a little light on capital ships, you didn't add anything that would help in sinking either German fleet, and you may be leaving yourself open against Japan since you'll be out of Western units within a round or two.

2 - Air (ftr to bom) + trn + ground units -
This is a little more flexible than #1, but it still leaves you a little weak in Western for a turn or two, and you still lack real Atlantic dominance until you can get your BB to the Atlantic.

3 - AC (or BB) + air + ground units -
This is a little more protectionist than #1 or 2, meaning your expecting Germany to at least keep an idle threat on the Atlantic (maybe they even bought a ftr/bom on G1) or the UK didn't buy an additional capital ship. The extra air also helps in hunting down the G Med fleet while you added some ground units for your existing trns.

4 - AC (or BB) + trn + ground units -
Very similar to #3 but you elect to go for a greater Afr presence in Rd 2 instead of adding to your air power.

5 - AC + air + trn -
Again, similar to #3 and 4, but might leave you a little thin in Western for a round or two, however you now have 4 trns on the board and are set in that area if you are going with a US to Africa shuck. This means you should have plenty of additional ipcs in later turns to continue to buy air.

6 - AC + air -
This is a more specific buy to counter an aggressive German move in the Atlantic. Coordinated with the UK you should be set to provided the killing blow at the tail end of a UK-US 1-2 or to deter a G fleet unification altogether. Your shuck is minimal for a round or two with your existing trns but there should be no doubt you'll have command of the Atlantic

7 - other -
I'm sure I left out some other Atlantic buys and I think Pacific buys would be better suited for a US Pac strat paper or KJF scenerio.

I usually look to buy a mix of land, air, sea on the early US turns, so I'll use either #3, 4, or 5 in most games. You don't need to over buy trns early so you do have some flexibility and you can get away with not buying a trn if you need to go to Sz 8 to help back up the British navy. I also like to always build some units in WUS to cover myself just in case Japan trys a landing in Ala/Wcan at some point.

The US shouldn't have much in terms of combat. The biggest opportunity might be at countering Pearl but I'd only consider that if Japan is left with 1 ac, 1-2 ftrs, 1 bb and only if Germany bought all land on G1. You can also look for a sneak attack on Sz 60 if Russia still holds Bury since your bomber and ftr from Hi can reach and then land there. But for the most part you are probably going to end up jumping right to NCM.

Your main focus is going to be backing up the British moves which means either helping out in Alg or reinforcing London with land and air. You want to get your air in range so you can help sink the German fleets, which is another reason I like early air buys. The UK can eventually hit the Baltic fleet and the US can hit the Med fleet, also if Germany reinforces its Baltic fleet you might need the extra US air to be used in a follow-up attack.

Other NCM are pretty simple, you can move your Sin troops if they are in danger and you should set up your Atlantic shuck. Place only what you need in Eus and the rest of your ground forces should be placed in Wus. Once you set up the Wus shuck it removes any serious threat (or annoyance) by Japan and if done right from US 1 it causes no delay in getting troops to Africa or Europe. I also like to move my Eus aa to Ecan right away just incase it is needed in Afr or in Europe on future turns.

Again the US probably won't have much action in terms of real combat in rd 1 or even 2, but it is important to coordinate your strategy with the other Allies and make sure you buy the right units early on so you are not left scrambling later.