Most people give up on yoga nidra because they fall asleep, and decide they have done it wrong. Before bed, falling asleep is not failure — it is the point. What follows is a plain thirty-minute script you can run from memory.
The script.
Lie down on your back, warm, covered, in the dark. Spend a minute simply feeling the weight of the body against the floor or bed. Do not relax on purpose; just notice where you already are.
Then move attention through the body, one part at a time: right hand, right arm, right shoulder, and so on down to the feet, then the same on the left, then the back, then the front. Name each part to yourself and move on. Do not linger or try to relax it. The naming is the practice.
When you have been through the body, return to the breath and count each exhale down from twenty-seven. If you lose count, start again from twenty-seven without annoyance. Most nights you will not reach one, because you will be asleep. That is the script working, not failing.