Boot from a live distro so you can modify your boot disk. Use the disk utility to create partitions. Copy the data to the relevant partitions ensuring to maintain file ownership and permissions. Modify /etc/fstab to mount the partitions at the designated locations in the filesystem.
I don’t bother putting anything but /home on its own dedicated partition, but if you ask 10 people this question you’ll get 12 opinions, so just do what feels right.