Whip control

When performing whips I can do the basic whips, but how do you maintain a perfect loop after doing multiple revolutions or slaps? Is there a certain technique?

only thing i can think of is zero string tension and make sure the string is gripped properly in you hand; by properly i mean with the loop ending on opposite sides of the hand. Sorry if i am not clear, try looking at the way they are holding the string in tutorials.