A number of different approaches you can take. What I do, I have a couple of separate partitions for data (documents, music, photos, etc.) that I can access from any installed distro. Then, besides the swap partition, I like to use 10 GB for / and 5 GB for /home for each distro. Edit fstab appropriately for easy mounting and access to all partitions from within each distro. As for grub2 and booting, I use customized scripts in the /etc/grub.d directory. On one computer, I use chainloader entries, but on another my customized grub entries boot directly into the other distros' kernels.
That's a quick summary. Be aware that if a distro like Fedora is involved, you may have trouble with permissions when accessing files from the other distros. When I install Fedora, I have to log in as root and run the following command:
# usermod -u 1000 -g 100 steve
That's something you might want to look into. I think you can run it from a tty terminal instead of from a root log-in, but I'm not sure.