The basic rules to qualify a person (beyond citizenship) is the 2/2/2 rule. This is standard for nearly every loan. It means that in order to qualify for a loan the applicant should have:
2 years work history (preferably in the same field);
2 year residence history, and;
2 years of credit history.
If you have the first two and don't have the third - sometimes FHA will allow for supplemental credit - that is, a verifiable payment history for items such as Fastrak, Cell phones, PG&E, rental history, etc. from which they will give the buyer credit for as they apply for the loan.
My recommendation would be to immediately go and apply for a Target, Sears or other card to help jump start that credit as quickly as possible. There are even Visa's and Mastercard's where you pay them $500 for a $500 line, use it and fill it up again - during which time the report to the credit bureaus to help give you that rating.
If you are very new here (less than 2 years), hopefully you have that international credit report - that may work as well.
Best of luck, John