How can I write a good RWBY Team CRDL fanfiction?

First, understand the characters. Know that Cardin is often the bully of the group, but there's more to him. Russel, Dove, and Sky also have their own personalities. You can start with a unique plot idea, like a mystery they have to solve. Maybe something related to an ancient relic in the RWBY world.

To write a good RWBY Team CRDL fanfiction, you need to be familiar with the RWBY universe's rules. Regarding their Semblances, you can either stick to the canon ones or come up with creative new ones for them. Also, don't forget about their relationships with other characters. You could create some interesting interactions between them and the professors at Beacon. For example, how they react to Professor Ozpin's strange requests or advice. This would add depth to your story.