Work yourself into submission.
One of two primary causes get me to sleep every night: habit or exhaustion. When it gets particularly late, I’ll go through my nightly routine, crawl into bed, and just gradually become tired by default. If, however, during the day I subjected myself to especially rigorous physical activity, then sometimes I’ll go to sleep earlier than usual, and pretty well at that. If your nightly routine isn’t ingrained enough to get you tired on your own, then the next best course of action is to wear yourself down with rigorous exercise!
When you’re trying to tire yourself out, cardio should be your primary weapon. It doesn’t even necessarily have to be intense; a pleasant evening stroll can raise your heart rate a bit and burn off some energy while also relaxing you. If relaxing’s not on the menu, try something more focused like jumping rope. Jumping rope will really get your blood pumping, and if you focus on counting reps, you get an effect not dissimilar to counting sheep.
Speed isn’t a requirement; if you’ve got some time, you can also try strength or flexibility training. Once, when I was moving into an apartment, I had to drag five boxes of assorted junk, a disassembled desk, and a full-size mattress up three flights of stairs. It was quite possibly the most exhausting thing I’ve ever done, but I slept like a baby that night. While you maybe shouldn’t push it as far as that, some weight training can burn up excess energy, while some stretches will loosen up your joints and muscles. You’ll be like putty at the end of it all.
A good sleep schedule is the cornerstone of a healthy lifestyle, but sometimes you gotta pump the gas a little to make it stick. Hopefully, your body will get used to being tired at particular times eventually, and then you won’t have to exhaust yourself anymore (unless you’re into that).