Putting Baby Down For a Nap

This is my second child and I did taking cara babies with my first. My first was such a great sleeper, probably part luck but also part of the foundation I laid with her. With this second child, I’m trying to remember everything that I did with my first but I must be doing something wrong. By the time my first was 4 months old, I could put her down for a nap and she just would fall asleep on her own, she didn’t need me. But this baby, she will not go down without some serious effort on my part. How can I encourage her to become a better napper?