@American:
In the US normally I buy at least 10 infantry on turn one, sometimes more. I use these to replace those sent to reinforce the South and Alaska as well as the islands.
The next turn is spent buying at least six aircraft, to replace the ones that went OCONUS on turn one to backstop HI, AK and Mexico.
If there is no attack on turn three then I buy a navy, at least three carriers and a couple of bullet stoppers. I then send forces to reinforce Canada, activate Brazil (on the way to North Africa).
Russia is
1- 100% Infantry
2- 50% infantry/ 50% tanks
3- 25% infantry/ 75% tanks
Past turn three really depends upon what is going on.
do you have some magical powers noone else has, because US can only produce 9 units on turn one. I prefer to buy 8 subs on US1.
US needs to build in the first 3 round a force that makes US able to have an impact as soon as possible, inf is not it (noone invades US, you dont need any units in canada or alaska. you want the axis to invade those places, it makes them use resources far away from their main objective, close to your productionbase.
To maximize US impact, if you are going for the atlantic, you need a force to stand against luftwaffe and shut down the italians a soon as possible, with probably 5 transports + loads as soon as possible.
in the pacifict you need to be able to stand against the japanese fleet off queensland as soon as possible. if you hold there, and stop him from taking hawaii, then you have stopped japan from winning.