The best matra I’ve found is “The Next time I’m dreaming I’ll remember to recognize that I’m dreaming”
The remember to recognize part is the key because you’re goal is to remember to recognize/relize you’re dreaming, not just to realize you’re dreaming, this is a small subtle difference bt it made all the difference for me. Until I made that change in my mantra it barley worked but now I can do it at will.
Also try repeatiing your mantra until you fall asleep.