Adding to Mike, also be aware that priorities follow the convention that the
bigger the number, the more important it is for the task to finish ASAP. A
priority 1 task is less important than a priority 3, not more important as
most people would usually think.
You can use 1, 2, & 3 if you like - and you have 997 more levels you could
designate if you wish to nail it down that fine. But the default priority
is always going to be 500.