I would like to install Debian on a USB drive and boot it from there. I have a USB drive with 64 GB of diskspace.

So I installed Debian Jessie (non-free) on it, and installed GRUB on the USB drive itself. Now I choose to boot from that drive, but it doesn't boot. The computer starts and I just get a text cursor blinking whenever I try to boot from it.

What else should one do to make such a USB bootable? Please advise.

If you require any additional information, please ask.