IP addressing for VPN

Hi, Can anyone please tell me what is the best pratcice for setting up IP addresses on a VPN? If I use 192.168.1.*** at my head office do I need to allocate a group of addresses from my this set for each of my sub-branches? (for example use 192.168.1.40 to 192.168.1.50 for sub-branch A) or do I give my sub-branch it’s own range ie: 192.168.2.*** at one branch and 192.168.3.*** at another?
Any help would be greatly appreciated, thanks