With most drawings, it's easiest to start them as basic shapes. Here's the top of the cello, just two rectangles.
Here's the top part of the body...
...and the bottom part.
Now start adding detail. The eraser is your friend!
After you finish sketching, color it in and cut it out. Then put on a concert with your dolls!
Hope you found this useful. If you have any requests for tutorials, please, please comment below. I'm starting to run out of ideas, and I have no idea what kind of things you want to know how to make.