What is the best meditation practice to fall asleep? I want to know if exist some practice to meditate when I am ready to sleep, in order to train while I am dreaming.
Maintain extraordinarily sharp attentiveness to your body as you fall asleep.  Your day-time meditation practice will have to be regular and consistent, without a daytime practice dreamtime practice will not really have a foundation to rest upon.

When you fall asleep, train yourself to stay aware of how all your limbs feel, the tension or laxity in your body, and the gentle rise and fall of your breath.

That is, in my experience, the best way to maintain aware levels of mind while falling asleep.  You must be able to observe without interfering too much, and that is why a daytime meditation practice is important.

If you set your intentions just before bed strongly, with the intent to further your practice and realizations in your dreams in order to bring ultimate benefit to all sentient beings and all that lives, you will make progress quickly.  There may be a few days where nothing happens, but if you keep to it, one day you shall break through.  As you fall asleep, keep your mind on your body energy and warmth, and you can use the physical body as an anchoring point for your attention until the falling away of gross perceptions takes place