IP Addressing in a WAN

I am writting a paper on a WAN design. I have 5 locations around the U.S. and 1 in China. I have them connecting via DSL to a VPN style WAN. I am having trouble coming up with an IP scheme for the locations. I have never fully understood IP addressing as far as design goes. I have to figure out the IP scheme as well as the broadcast addresses and subnets. Can anyone give some advice.