At it’s core, MILD is just setting your intention to remember to realize you’re dreaming. You can do this anytime. It’s based on prospective memory, remembering to do something in the future (such as question reality or do a mindful RC).
MILD has worked well for me when I am able to connect my mantra to something I expect to experience/see in my dreams (such as my dream signs). For example “When I encounter water, I question my reality.” (Of course this only works if I follow through and question my reality in WL when I encounter water, too).
I also use MILD mantras to help me remember my lucid intentions: “When I realize I am dreaming, I will X” where X is whatever my goal is.
I feel like I’m always linking people to this thread, which gives a lovely discussion on MILD mantras.