This is the most common mount point that people move to a different partition after they have already installed ubuntu on a single partition. As such, there are several guides on how to make this change, including one that I have written myself. The advice in these guides can generally be applied to moving any mount point to a separate partition.
Generally, people allocate as much as they can to /home, so just allocate what you need for every other partition, and then the rest to /home. See the section of this article on /home for more info. Take heed to ignore the comments about the possibility of using vfat as the filesystem type for your /home. This is incorrect advice, as /home must be on a partition type which supports permissions, like ext3.
Guides on moving /home to a separate partition
http://psychocats.net/ubuntu/separatehome This is the default suggestion given on IRC in #ubuntu