We started a bedtime routine for DS when he's 4 wks old. We bring him upstairs to our bedroom at around 9-9:30pm, very dim lights. Nurse, diaper change, swaddle, then nurse again. If he's drowsy/sleepy, we put him in the crib. If he's still awake, we sing/rock him until he's drowsy or asleep and put him in the crib. Has been working pretty well for us so far (knock on wood).
We bathe him 3x/week, on those nights, we start bath time at 8:30pm then bedtime routine after that.