See ? I told ya to give it a go!
Being a first drawing I can't critique much, it's like beating a dead horse, but small steps improve so here are things to bear in mind for next time.
The hair sits a little too far off the top of her head. I can see what you were trying to do, but this makes it look like her head might be a little out of shape.
The neck is also a little on the long side. But that comes with practice.The arms aren't too bad either. Normally they come down to about mid-thigh level on most people.
Hips. Generally women have wider, more rounded hips. Wider than the shoulders in particular. Bear that one in mind.
As for copying from other drawings; don't worry about that. It's a good way to begin, it offers practice and quite honestly, I doubt there are many people who haven't copied from other drawings before. I myself, owe a lot of what I've learned to other artists simply by looking at their work for ideas, fixes, methods, etc. There is no shame in it. Never forget, it's how portraits tend to be painted as well.
Also, allow me to relieve you of one misconception. A lot of people get into manga because they are led to believe it's easier to do than other, more realistic methods. As someone who is gradually moving into more realistic territory, I can tell you they are wrong. No matter what you choose it's difficult either way. It's simply a matter of practice and putting the effort in.
Anyway, do more please.