[littlehamster]

A bad blow job starts with sucking and scraping against the clitoris right away, or even using your teeth. A more common misunderstanding is thinking "licking the spot" means "sticking your tongue inside the hole," leaving the clitoris untouched, so she only feels being stimulated but not really getting off.
The key to oral sex is getting your partner wet, starting slow and building up, maintaining a steady rhythm, and listening to her body language and breathing.
Here's a quick tutorial we came up with with my girlfriend.