From https://forum.mikrotik.com/viewtopic.php?t=87458#p439462 
Thread, Configure multiple subnets with DHCP

By h4ni8all
Tue Jul 29, 2014 6:43 pm

Hi, this should get you started:


/interface bridge
add disabled=no name=LAN-bridge
add disabled=no name=LAN2-bridge
add disabled=no name=LAN3-bridge
create bridges for start.

/interface ethernet
set 0 disabled=no name=ether1-UPLINK
set 1 disabled=no name=ether2-LAN
set 2 disabled=no name=ether3-LAN
set 3 disabled=no name=ether4-LAN2
set 4 disabled=no name=ether5-LAN2
set 5 disabled=no name=ether6-LAN3
set 6 disabled=no name=ether7-LAN3
prepare your interfaces. I just added two in each subnet. you can add more as you need.

/ip pool
add name=lan ranges=10.0.0.10-10.255.255.254
add name=lan2 ranges=192.168.0.10-192.168.0.254
add name=lan3 ranges=172.16.0.0-172.16.255.254
Create dhcp pools. 

/ip dhcp-server
add address-pool=lan disabled=no interface=LAN-bridge lease-time=1w name=LAN
add address-pool=lan2 disabled=no interface=LAN2-bridge lease-time=1w name=LAN2
add address-pool=lan3 disabled=no interface=LAN3-bridge lease-time=1w name=LAN3 
create dhcp servers.
 
/interface bridge port
add bridge=LAN-bridge disabled=no interface=ether2-LAN
add bridge=LAN-bridge disabled=no interface=ether3-LAN
add bridge=LAN2-bridge disabled=no interface=ether4-LAN2
add bridge=LAN2-bridge disabled=no interface=ether5-LAN2
add bridge=LAN3-bridge disabled=no interface=ether6-LAN3
add bridge=LAN3-bridge disabled=no interface=ether7-LAN2
associate each port in its respective bridge.

/ip address
add address=10.0.0.1/8 disabled=no interface=LAN-bridge
add address=192.168.0.1/24 disabled=no interface=LAN2-bridge
add address=172.16.0.1/16 disabled=no interface=LAN3-bridge
Set up the gateways for your subnets.

/ip dhcp-server network
add address=10.0.0.0/8 comment="lan" dns-server=8.8.8.8 gateway=10.0.0.1 netmask=8
add address=192.168.0.0/24 comment="lan2" dns-server=8.8.8.8 gateway=192.168.0.1 netmask=24
add address=172.16.0.0/16 comment="lan3" dns-server=8.8.8.8 gateway=172.16.0.1 netmask=16
create dhcp servers



After this you're local side should be set. All you need now is NAT and set up your uplink towards ISP on ether1. Since I have no idea what kind of connection you have from them , its impossible to write anything.

HTH.

regards,