I wouldn't exactly consider myself a professional, but I seem to have stumbled upon a pattern of behavior that, without fail, puts me in a lucid dreaming state. They used to be random, but this is pretty much as close to "LDing at will" as I think I'll get.
Maybe this would work for others, but I was lucid dreaming as a kid before I even knew there was a name for it, so I'm pretty sure I just hit the biological lottery.
Back in college, I used to take shit like Adderall to help me work through the night and actually get shit done, resulting in sleepless nights. I knew for a fact that, after pulling an all nighter, whatever nap I would take in the afternoon, say 12pm, was going to be a lucid dream. It's a fucking awesome feeling. "Waking up" in the same room you fell asleep in, rising out of bed, glancing at a window, then looking down, then looking back out again to find a whole new landscape is usually my tell. Upon confirming lucidity, I like "creating" new rooms within my house filled with whatever it is I desire. I've dreamt up rooms filled with drugs and have consumed them--to rather interesting effect. (Shrooms actually gave me visuals. Heroin slowed my pace down but lacked that euphoric punch.) Flying also feels fucking amazing, I've caught a bird's eye view of my city many times over the years. Never, ever gets old. It's gotten to the point where I've mastered the art of dream manipulation, so lately I've been reading around to see what other Lucid Dreamers choose to do with this precious, beautiful state. I know I've only scratched the surface, and I want to know what other unimaginable things can be achieved.
To summarize- I've taken Adderall or meth and, after coming down the next afternoon, take naps that become lucid dreams. I'd still get LDs as a kid and through my teens without stims, but this seems to be a pretty reliable formula I've stumbled upon, for whatever reason. And no, staying up without stims and then napping does not produce LDs for me, it seems to be left up to chance without the drugs.
TL;DR Adderall and meth generate LDs for me on the naps I take during my comedowns. Doubt this will work for everyone though, as I've been Lucid Dreaming since I was a kid, along with bouts of sleep paralysis.