1) Deposit your down payment money into a bank account and let it sit for at least 60 days.
2) Do not make any large deposits or withdrawls from that account within the 60 day window.
3) Have your loan officer do a credit check now to see if anything needs correcting before its time to purchase.
4) Do not open any new credit cards or make any large purchases such as a car or furniture.
5) Finally...don't get fired from your job unless you have another lined up.
Your loan officer will discuss the available loan types to see what is the best fit for you. Good luck,