You've got a really lovely range of tones here, so the mono did indeed work well!
There's certainly scope to refine how you compose pictures, in a couple of ways.
First, there's a standard idea (which you don't always need to follow, but it generally works reasonably well) that you should put the main centres of interest on the "thirds" - the four points in the image that are 1/3 of the way up/down/across the picture. These places are strong, and what is sitting on them is emphasised.
Here, if you had framed slightly to the left, the model's face would be on one of the thirds, approximately, and her arm reaching along to another one. If you'd cropped a little at the bottom, it would be pretty exact (and, more importantly, would look good!)
The other obvious thing is to be careful where you cut limbs off. You have one hand and two legs with feet out of frame. The legs are not an issue, as they're dark, and not very obvious in the picture, but the hand is. Cropping above the wrist would work, as would having hte hand entirely in the frame, possibly by having the model lay it along her hip.
These aren't Rules, never to be broken - but they're reasonable guidance, to break when you feel it benefits a picture. Sometimes, you do best by deliberately doing the opposite of the rules, of course.
It looks as if you've used a flashgun on the camera, giving very harsh shadows. The model's complexion is so good this doesn't matter - the facial tones are perfect - but often softening the light by bouncing it off a card, the ceiling or a purpose-made umbrella gives a gentler look.
And for those lovely tones, and the assured expression, my vote.