1. DONT START WITH YOUR PENIS. Go VERY VERY slow, and build up with fingers. one finger for a bit, then two. Once you start pushing a third, and she hasn't refused (point 3), then you can try your dick.
2. Lube lube lube lube. Lube your fingers lube your dick and lube your soul
3. Most dogs don't like it, most commercial porn is forced, if she says no, it means no, and don't be surprised.