Hey Ji Li, Welcome!
There's been a lot of good advice in here already.
Drawing is probably the most useful skill anyone can have no matter what you do. =D
Definitely liking that you are taking the time out to practice basic shapes. Make sure you check the tutorial section there are some great tutorials there by loads of people. Specifically Ron Lemen's (Aka Fred Flickstone) Tutorials on the figure. Over Here
I'm curious if you're currently holding the pencil, the same way you hold it when writing? If so, then check this out Pencil Grips
People often overlook how they hold the pencil as they're drawing. Its actually very important in developing control. I suggest using the Violin Bow Grip or Gesture Grip. It allows you to work quick and use your entire arm instead of just your wrist and/or elbow. Ofcourse it's easier if you have an easel or have the surface tilted up. towards you so you have room to move your arm.
Remember stay loose early on in a drawing, take a breath, don't be too tense. Drawing is as much about feeling as it is seeing. I'd suggest if possible that you take figure drawing and do fast gestures. People will tell you to basic shapes before doing the human figure. There's no CORRECT way to do it, IMO learning the human figure through basic shapes allows you to draw anything else. Simply because the human body has every shape you could imagine. Its also arguably the hardest thing to draw (and have it look right) because of all sorts of psychological hurdles, but I've said too much. Keep Drawing! More Chi! Train Harder!