Take the lead from your baby. I don't think you need to "introduce" a routine, rather you watch your baby and see how they react to different things and if they seem to be doing things at a regular time, and work with that. At around 2 months old we noticed that DS seemed to fall asleep around 8pm (when it got dark) regardless of what time we had started putting him to sleep. So then we created a bed time routine around that- bath, cuddle and feed starting at 6:30pm. He still does that every day but it has moved a bit earlier, as we noticed he was falling asleep earlier.

I thought I should maybe introduce a bedtime routine earlier, as lots of my friends talked about giving baby a bath before "bedtime", but before 2 months he didn't really have a "bedtime", it was more like 3-4 hour cycles around the clock.