It depends how vivid and consistent the scenario and image of it are, in my experience. If you get caught up in scenarios that start forming while trying to drift off to sleep, more often than not it's either just dialog or the range of experience is very limited, with almost no visual aspect, they aren't stable enough to be useful for much other than more easily falling asleep (which is a requirement somewhat overlooked when people try and WILD, getting yourself to fall asleep is extremely important--losing consciousness in the process isn't always a given).

However, if you find that you are witnessing what would otherwise be a dream scene driven all on its own, only you aren't actually dreaming yet (it's as if all you can do is see and maybe hear, and you are still aware of your physical body and lying in bed), that's what will almost guarantee you success. I typically only get these self-driven, stable, visually vivid scenarios when I just wake up from a dream and I'm still in a hypnagogic state, more or less. If you don't do anything to interrupt the scenes/scenario from playing out, at a certain point you should simply be able to "step in" to what's going on and it'll actually be a dream from that point on. For me, knowing when to step in is something I can just feel or know, there's no way I can actually going about explaining how I know when the moment is right. For all I know I could enter right away, but typically I wait a good 30 seconds and even up to 2 minutes sometimes when I actually have the opportunity to get an LD this way.

When I say to "step in" to the scene, it's not anything that involves the tactile sensations of stepping or anything like that. The scenes are already like watching a movie play out in front of me, from my own first person perspective, only "I" am not actually in the scene (and the moment "I" enter it, it becomes a dream). All I do is sort of will myself to take my place in what I'm seeing and make it instead something I fully experience.