To determine how far apart you should place your recessed lights divide the height of your ceiling by two.
So if your ceiling height is 8 feet then you should space the recessed lights 4 feet apart and if your ceiling height is 10 feet then you need to space the recessed lights 5 feet apart between each fixture.
So in short you should space the recessed lights 4 feet apart when you have an 8 ft ceiling and for a 10 ft ceiling you should space the recessed lights 5 feet apart.