ok, i've been trying to work with the photo but it's hard b/c it's dark and small, so i'll try to explain... let me preface this by saying that this is what i would do if they were my brows. i'm not telling you how to achieve the look that you posted.
that being said, what i would do is start where i put the yellow square. take the brow "in" a little from the inside, making the area where the brow starts and is flat at the bottom a little narrower. i'm talking minute amounts at a time here, of course!
then, where the red square is, i'd stay along your natural curve @ the bottom but bring it down a little, so the arch isn't so high. be careful, as this is tricky business and if you get too gung-ho about it you can flatten your brows.
at the green square, it's hard to see in the photo, but it looks like the tips of your brows dip down a little, emphasizing the arch. i'd possibly tweeze/wax/whatever from underneath ever so slightly if needed after dealing with where the red square is. it might not even need it after that.
if this makes no sense, get me a bigger and brighter pic and i will gladly mspaint it up for you!
