Control stays with you
The safest way to learn this skill is to stay in control of depth and speed. Positions where you lead, for example kneeling or lying on your side, let you move forward and back at your own pace. A partner keeps still unless you ask otherwise. You agree on a hand signal before you start, because speaking is not always possible. Progress comes from small repeated steps, never from pushing through discomfort.
Pair it with Breathing, Relaxation and Positioning and read the how to deepthroat guide.