I would suggest reading some poly books. A big part is coming to terms with feelings and situations you may not have encountered before.
One approach is to imagine a lot of situations and swap things in and out of that situation to see how you would feel. Foe example, imagine if she came home and said she was attracted to a guy she knows. See how you feel. Then swap it out. Imagine if you had said you saw a girl you were attracted to? Or imagine if she said she saw a girl she was attracted to? Or imagine if she saw a TV star she was attracted to?
Try to vary the situation to see where your comfort zones are and then you can try to understand them. Over time, some uncomfortable situations may not be so uncomfortable as you get use to it and trust grows.
The biggest area to focus on in the beginning is communication. Try to take some things slow so both sides can adapt.