Mikrotik doesn't actually implement DHCPv6 server. So you have to use SLAAC. Let's assume you're getting IPv6 prefix from ISP via DHCPv6. So you need:
/ipv6 dhcp-client
add add-default-route=yes interface=WAN pool-name=ipv6-pool request=prefix
/ipv6 address
add address=::1 eui-64=yes from-pool=ipv6-pool interface=LANbridge
The config for DHCPv6 client is requiring IPv6 prefix from ISP and stores it into address pool.
The IPv6 address setup sets LAN IPv6 address to be the first address from pool. E.g. if you receive prefix 2000:aaaa:200::/60 from ISP, then router LAN will (most likely) get address 2000:aaaa:200::1/64. By default, Mikrotik runs routing advertisements via all interfaces, hence it will send RAs to LAN. Connected devices will pick it up and invent SLAAC addresses (using correct prefix and adding random bits to the right).
If you want to have deterministic addresses on LAN devices, then you'll have some work to do ... either you'll have to set addresses statically on end devices or you'll have to install a proper DHCPv6 server in LAN (ISC DHCP server, as shipped standard on modern linux distros, will do) and configure static leases there. in any case, if ISP gives you different prefix, you'll have to change many settings :-(
On WAN interface router doesn't need any global address, link-local address is probably enough (at least it's enough in my case, my ISP is using PPPoE ... in case of IPv6oE might be different).
If your ISP is giving out prefixes with length 64 (mostly good enough for single IPv6 subnet) and you have to use one of addresses for WAN interface (yes, that's also possibility), then you're out of luck, it is not possible to divide /64 prefix to two subnets (one used on WAN interface and another one used on LAN interface).
Could be that you have to configure DHCPv6 client to actually
request=address,prefix if ISP requires global IPv6 address on your router's WAN address.