I was sketching abit to relax, and decided to compile it into a tutorial-ish thingy.
Tips I picked up to sexify your female chars:
1. Curves curves curves. I'm not just talking about her bod, even her POSE must be curvy!
(NOTE: Avoid having the Head, Shoulders, and Hips in the same line on the canvas. Likewise, the shoulder and hip angles should not be straight. Tilt them angles!)
2. Avoid straight lines and use gentle curves for the entire body. The more curves there are, the less hard edges there will be; and the softer she will look.
3. Open her mouth a teensy-weensy bit for the added sensuality. Have different levels for the eyebrows if you want moar seductiveness.
4. As for all drawings, get a strong silhouette!
5. Curves curves curves.
These little tidbits have sexified tons of drawings for me. You don't need big boobies to sexify a girl.
Don't believe me? Cover the boobs on the drawing up there.