You really don't want to force every
application to go to 'other than C'. Some things you do want on the boot drive.
Yes, you can mess around in the registry and change it, but then for the things you want on the boot drive (AV, utilities, etc), you have to manually select. So either way, sometimes you have to select which drive.
For Steam, you can designate multiple targets.
For applications, just choose....
For all other stuff, see these tutorials:
Win 7 & 8: http://www.tomshardware.com/faq/id-1834397/ssd-redirecting-static-files.html
Win 8.1: http://www.tomshardware.com/faq/id-2024314/windows-redirecting-folders-drives.html