Yep, before you start shading or anti-aliasing, make sure the form is correct. For basically everything, especially if you're a beginner, use a reference. That's the best way to learn. The artists who are best at drawing humans have studied anatomy like you wouldn't believe.
So don't just draw it out of your head yet. It takes years to get there.
Get some good line art going, then we'll see about the shading.