The best is to check it first thing in the morning, when your car has had all night for the oil to drain down......It takes Ford motors forever for the oil to drain from the top, down to the pan.
By doing this you will get an accrate level of oil.
Personally I check it everytime, I have the hood open. usually 1 or 2 times a week
But I tend to be really anal about my cars, and keep them in good running condition