1. Pick a bedtime you’d like them to stick to at some point, and create an obvious difference between daytime and nighttime.
We started the first week of my son’s life, by introducing a sound machine (specifically the heartbeat noise) that we played at 8:30pm every night when we laid him down for a nap. He slept in a bassinet in our room, but we turned the lights low and turned the tv down. Basically, we created a peaceful, quiet environment at the same time every night and gave him a noise to associate with being sleepy and calm. I’ve read that people will introduce loveys that they only give at bedtime for the same effect, which I think is a great idea! Start as young as you want, and do it every night around the same time (with some exceptions, like sickness, people visiting, etc), EVEN when you know it’s going to fail. If you lay them down, and they cry immediately, pick them up! It’s okay, and it’s not a failure. You still went through the motions and let them know that at a specific time, the lights will be dimmed, a sound will play, and they will be laid down with the intention of getting them to sleep. Sometimes they’ll even surprise you and fall asleep right away!