Well I am in a graphics sort of mood tonight so I decided to do a quick little drawing of how I have come to shape my own eyebrows. Maybe it will help you a little? I started out with this tutorial
http://hairremoval.about.com/od/eyebrowshaping/ss/eyebrow-shaping.htm and over time kind of tweaked the shape to my exact liking. I went really really slowly with it, taking little bits away at a time whenever I would tend to my eyebrows. It made for a really smooth gradual transition.
Here is basically what I do now:

It seems to me with shaping your eyebrows as an MtF, there are two main goals:
1) raise the lowest point a little (females tend to have higher set brows) and
2) add an arch shape (tends to distract from or beautify excess brow bone)
I hope this helps you! In closing my only other advice is take it slow and good luck!! You will be stunned at the effect it will have on your face... I can already see it

Also, note the area that I typically leave untouched. Taking away hairs there can make things look a bit unnatural. As well, you don't want TOO much arch, or you will look like you are angry or something

I would refer to the tutorial for just the right amount of arch.