These are good first attempts. But you asked on what you can do to improve so let me give my suggestions.
To start off with, get closer, much closer. Or, if you want a loose fashion-type of composition, include more of the model's body.
Second, open up that lens to blur the background more. And in the BW shot, move the model further out from the background.
Third, watch clothing and hair. The hair and jacket need adjustment in the color shot.
Forth, the pose. Much better in the BW than in the color shot. Try not to have the model leaning away from the camera. Be careful of double-chins, neck wrinkles and head tilt. Watch for cutting-off parts of limbs as the tree trunk on the left does in the color shot.
Fifth (and, ultimately, the hardest) is expression, which includes mouth, eyes and overall facial tension. In the color shot she looks uncomfortable. In the BW her smile is just a bit big.
Sixth: Camera position - good in the color, too low in the B&W.
Seventh: Eye catchlight. Not essential, but it is usually a good idea to bring life to the model's eyes. Think of this as the finishing touch. You got it in the BW but didn't in color.
Finally, post processing. Different crop and some blurring of the background would help the color image. For the BW, a tighter crop, reducing contrast and eliminating the blue tint would make a huge improvement. Never tint people blue unless you intentionally want them to look dead or cold.
I think the B&W shot can be re-processed to much better effect. You don't say whether or not image editing is okay, so let me know if you want to see my ideas on how this could be processed.