An IPv6 address has 128 bits. The last 64 bits represent the interface ID. Usually an organization gets a /48 prefix. So you have 16 bits remaining to subnet according to your individual network.
The rules for subnetting are in general the same as with IPv4, you will try to look at perfix aggregation, subnet consistency, security considerations (access rules) and network growth.
Before you finalize any addressing plan, make sure you got that conservative IPv4 address space thinking out of your cells… 😉
Hope this helps