I only achieved a light trance, how can I go deeper?

Practice. By entering trance frequently, you train and condition your mind to enter deeper and deeper trances. It is the same as a runner who trains for a marathon. He starts with a short run, followed by progressively longer runs until he builds up the stamina for the full-length marathon. (Also, make sure you turn off your cell phone and make sure you won’t be disturbed during the trance.)

You can also practice several component skills, like focusing your attention, listening, and visualizing. For more on this, read, How to Become a Better Hypnotic Subject.