"My girlfriend is terrible at blow jobs. So so bad. It's like she's gently nudging it with a damp teddy bear. I don't want to hurt her feelings, but I'm always seeing people saying you have to 'teach your partner' what you like. How the hell do I do that?"
Take a banana and suck and lick and mouth it the exactly same way you want her to do it to you. Do this on the bus.