When he can't forget your name... that's when you know you are doing a good job...
Oh and moaning... thrusting... lifting himself up a bit... grabbing your head... and begging for more are all signs of a good blowjob.
"The weakest soul, knowing its own weakness, and believing this truth that strength can only be developed by effort and practice, will, thus believing, at once begin to exert itself, and, adding effort to effort, patience to patience, and strength to strength, will never cease to develop, and will at last grow divinely strong."
- James Allen