Dave Elman developed a few really good deepeners to deepen the state of a hypnotic trance.
By far the easiest is the hand drop deepener.
“When I drop this hand into your lap, you will go X times deeper”
Pick up your subject’s arm by the wrist and drop it gently into their lap.
You will find it easier if the X is ten or below because its much easier to count to ten or imagine ten items than it is a hundred or a thousand. You can count to ten on your fingers or your toes, its much harder counting higher than ten.