Rule 1: don’t use VLAN ID 1
If you want to seperate networks (at least, I think that is the main reason for having multiple subnets), you might want to consider using VLAN’s. Especially in the correct way, as described in the “Bible on VLAN”:
http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1