Many people swear by routines, and to some extent they are important. But my baby is 6 months and has never been given a strict routine, as she is constantly changing her own routines around, everytime we settle on one. At 6 months she seems to be settling into her own routine, to be honest.
We let her nap whenever she wants in the day, and we find she takes them around the same time every day now.
We tried putting her to bed every night at 8pm after bath and book; for 3 weeks while we did this she screamed every night until she wanted to actually sleep. 3 WEEKS. Now we do messy food play, then bath, then book and last feed and she's calm after that, puts herself to sleep around 11pm. That's late, yes, but if we put her to bed before that we know it's just hours of screaming. 3 days it's supposed to take for a routine to settle, apparently.
The evening routine of messy play, bath and book only started happening about a week ago when we started weaning, and it happens between 6 and 8pm each night.
Some people might say that perseverance with routines would make our nighttime's a bit easier, but we persevered for 3 weeks and all we became was more stressed and upset. Letting our 6 month old set her own routine means we're all alot calmer and she has settled herself into what she's comfortable with.
My point being that while a routine WOULD be helpful and will be important as she gets older, at this point, based on our baby, we know there is little point trying.
As to HOW, well, we did try bathing her every night but couldn't find a reason for it; she doesn't get dirty. So allowing her messy play means she needs a bath afterwards, and that system of one following the other is, in itself, a routine. You just have to do things in the same order every time. Not necessarily at the same time every day, just in the same order, so they learn what to expect.
Hope this helps, best of luck x