Apologies for the glut of technical posts - normally I drop this kind of thing onto my PhD wiki but it's not available atm :(
1) Setup the shared folder on the host by bringing up the settings dialogue for the appropriate VM within VirtualBox. Click 'Shared Folders' and set up as required with a particular name. Remember the name you've given the folder.
2) Start the VM. Make a new directory in /mnt, this will be the directory to contain your shared folder content. E.g.
3) Type the following command into your terminal:
sudo mount.vboxsf *name_created_in_1* /mnt/*folder_created_in_2 *
sudo mount.vboxsf my_docs /mnt/docs_host/
All done! You should now be able to do an ls on the directory you created in 2) and see the content you linked to in 1).