Her ponytail is too stiff.
Try separating the strands a little more so they fan out in different directions.
Also, her blush is too thick.
I think you might be pressing on the pencil too hard.
You should be able to see each individual stroke of your pencil and leave a tiny space between each stroke.
(There are a ton of diferent types of blushes to choose from, you should experiment to choose your favorite.)
If you need a reference, go to your local library and look through different manga books and I assure you that you will find so many references of girls blushing, even guys, your head will spin.
Also, the anatomy of her face is off.
While you're at the library, you should go look at a couple of anatomy books as well.
One more thing, try to thicken her neck out a bit more.
I'm not sure if you wanted me to critique the guy, so I won't say too much on him.
First of all, the horizontal guidance line is crooked.
Secondly, the point at where the two lines intersect should be where the nose is, not the mouth.
Keep practicing, and over time, you will be able to see an improvement in your drawings.^^