Help booting live disk

[Linux for blind general discussion]

I've never successfully booted from a USB stick, but regarding booting
from an external optical drive, I once had a laptop that wouldn't wait
long enough for my USB powered external optical drive to power up
before the laptop would boot from the hard drive. As a result, I had
to either reboot from the running system or hammer ctrl+alt+del as
soon as I powered on the laptop until the external drive was at full
spin to boot liveCD/DVD or installation media.