It is normal to kiss women on the breast(s) once the sexual relationship has developed beyond just kissing. But always remember that the freely given consent of the owner of the breast is required in...
Go slow, don't make her uncomfortable, Slowly take her shirt off, then hug her and kiss her and then while you are hugging her take off her bra, then just start kissing her neck and make your way...
No different than a guy kissing a girl or a guy kissing a guy. Take it slow and if she likes it you'll know what to do. Kissing is a quick learning process