How can i get myself into the habit of sleeping early without having a fixed bedtime?

Sleep hygiene: First practice sleep hygiene (type term in browser for details). Take melatonin two hours before desired sleep time. Purchase and faithfully wear blue-blocker sunglasses to block stimulation of the ganglion cells of the retina which, in bright light (such as in front of a computer like I am now) send a message to the brain that it is not time to sleep. No caffeine and no alcohol.