Depends on a few things. Where is your weight set? Is the opponent attacking your front leg? Etc.
Generally, if you mean to leave the same foot out in front after your move, then you want to move the back foot around and behind the front foot. They will not cross. The front foot is a pivot that the back foot "spins around".
If you mean to change sides as you move, then you would move the front foot around and behind the back foot (which will become the new front foot). After the front foot has slid back to just behind behind the back foot, the back foot becomes the "pivot", and the the other foot completes the spin as above.
Hope that makes sense.
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin