@VooDooMedic There are two ways. But this is mostly and strictly liquid and chemical related. If you work with chemicals ALWAYs keep the pant legs out as you do not want drainage into your boots. The same applies with general liquids. While the bottom of your work pants will be wet the inside of the boot remains relatively dry.
If however you do not work in wet or chemical filled conditions I suggest tucking them so long as no circulation is cut off to your legs.