Questions about blood sugar, insulin and burning off glucose

I understand the basics about glucose and insulin in that if your blood sugar hits a certain point your body will release insulin into the blood stream to take excess glucose to the muscles or fat cells. I also know that you can't burn any fat while insulin is present in your blood. I simplified things to my understanding that your body runs off two fuels, glucose and fat. Stored fat is a combination of glucose, primarily, saturated fats and protein. So basically if your body has too much of glucose it will just store it as fat. My question is which process does your body use when it is burning calories/glucose? Does it go with I FIFO or LIFO?