How do I give hickey? Help??!!

So I've been seeing this guy and he always gives me hickeys on my chest and I've been wanting to give him some but I'm not able to do so. I've been practicing on my arm and I can't give myself a hickey, they disappear two seconds later. I've seen every youtube video, article on the internet, asked my friends and they all tell me to suck the skin. And that's what I do but instead of sucking my skin, I suck my lips and I don't know how to position my mouth to be able to suck the skin and suck hard enough...

Edit: I don't need you to tell me they're trashy, I just want to give a hickey... ahaha