QUOTE(XPAWNED01 @ Aug 17 2011, 01:53 AM)
you dont really need to, if the body proportion is the case. it's not like i started drawing yesterday.
Actually
I wanna draw the girl with her body twisted a little bit. Maybe that's the problem I think.
Thanks for the advice anyway. I appreciate it.

That's where the anatomical problem is.

Frankly, unless she's a gymnast and/or double jointed, she can't twist the body to that extent. You can feel this yourself: lie down on a flat surface (bed or floor, doesn't matter), on your back, with your chest facing the ceiling. Then, making sure your shoulders remain touching the flat surface, twist your lower body (legs and hips) to one side.
You'll find that you can't really turn your torso and lower body to more than a 90-degree or right angle turn to each other (that is, your chest/torso facing the ceiling, your hips twisted to the side). Unless of course, as I mentioned, you're extraordinarily flexible. Even then, not more than a 120-degree angle. Any more, you risk snapping your spine. >.<
Anyway, point I'm trying to make is that considering the angle of her butt, you should only be able to see the side of her body. Certainly not both her breasts at the same time!

Not my tutorial, but the angle illustrated in this manga drawing tutorial fits closely enough to your sketch, with just some slight differences (the character in the pic has her arms facing forward)
Female perspective tutorial, by legendra on deviantArt