If you lucid dream every night you may find Tibetan Dream Yoga interesting. It can be secular or spiritual since it is a Buddhist practice.

See this book by a well-regarded teacher for more information: https://www.amazon.com/Tibetan-Yogas-Dream-Sleep/dp/15593910...

Although not the same as lucid dreaming, I’ve found practicing yoga nidra has helped with my own lucid dreaming: https://en.m.wikipedia.org/wiki/Yoga_nidra

There is also a book “The Tibetan Yogas of Dream and Sleep” that has some techniques I’ve found helpful for lucid dreaming, although it describes it in the context of Tibetan Buddhism, which may be off putting for some: https://www.amazon.com/Tibetan-Yogas-Dream-Sleep/dp/15593910...

Another common technique is to ask yourself at various points of the day “is this a dream state or waking state?”. Then, if it has become a habit, you may ask yourself it when you’re asleep and trigger lucid dreaming.