Like others have said, a bedtime routine is a good way to start.

We started ours around 6 weeks old and he got into it fairly quickly and it really helped his night-time sleep. For us, it was bath, PJs, bottle, bed.

We did the sleep-eat-play routine during the daytime as early as we could, and we have kept that up even to this day, and we kind of let him day-time routine evolve around that framework.