Migrate OS to smaller drive?

[vr <debian-user@iotk.net>]

What's the best mechanism to migrate a working bootable system from one
drive to a smaller capacity drive?

e.g. take this 226G filesystem

df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sdb1             226G  4.1G  210G   2% /
tmpfs                 3.0G     0  3.0G   0% /lib/init/rw
udev                  3.0G  244K  3.0G   1% /dev
tmpfs                 3.0G     0  3.0G   0% /dev/shm

and transfer it onto say a 32G drive?