1st step, mag-decide ka kung bridge mode yung pldt modem/router o hindi. Bridge mode setup is a little bit complex vs non-bridge. Advantage, iwas double NAT.
Kapag hindi naka-bridge mode, magdo-double NAT yung network mo which is not good.
2nd step, allocate different IP subnet sa bawat interfaces ng mikrotik.
3rd step, enable DHCP on all interfaces except sa WAN port (yung connected sa pldt modem/router).
4th, setup your access control, eg firewall, bandwidth control etc
5th, optionally setup your own dns resolver.