Romyrick,

What you ask is a very broad question. However you have come to the right place to find answers. Perhaps I can lead you to a few resources that may help. Below are a few of my favourite threads on the subject of domination from the forums. You will find many more if you browse around the knowledge base and my BDSM life sections of the forums.
http://www.bdsmlibrary.com/forums/showthread.php?t=7668
http://www.bdsmlibrary.com/forums/showthread.php?t=9542
http://www.bdsmlibrary.com/forums/showthread.php?t=9300

There are dozens more scattered around the place. You won't learn everything overnight so take a few deep breaths and start reading and thinking. I consider myself very much a beginner which is why I'm not trying to give you any hard and fast answers. Wander around the library and read a lot. The information you want is here but it will take someone with more experience to summarise it for you.

The only practical advice I can offer is talk to her, talk until you lose your voice then talk some more. Show her that you are taking her concerns seriously and that you are working on it