What is something that you need to keep in mind when studying to become a labor and delivery nurse?

Anymore hospitals want to see that you are not only certified in BLS for providers, but also advanced certifications for specialty areas. For L&D, ACLS & NALS FOR ADULTS AND NEONATAL CERTS in addition to being an RN. Some will give you 6 months or so to get certified if you are not. You can also be an asset if you get involved in LaLeche instruction, prenatal class instructor. Sibling classes. Lots of options here.
One piece of advice I would offer is that this specialty is usually filled with happy moments for families and you. However, when there is a bad outcome, whether MVA, anencephaly, or otherwise, it can be very profoundly Sad! The family,and often staff even, will look to you the professional to get them through the experience in the best way possible. Even perhaps with a few good memories. Some hospitals do high risk l&d's. some midwife's have different settings.
This answer is based on my experiences. Hope this helps.