Paper

Drawing paper is a great way to practice your line work and value. 

Notice how abstract some of the shapes can get while still maintaining form. 

Make sure to use a light source and be sensitive. 

Good luck!

Here is a great way to start.

Get it all blocked in before adding value.

Things to consider:

Crisp lines

Contrast

Interesting shapes

Negative space

Ground plane

Soft and hard transitions

For those of you who think this is just for beginners
 check these paintings out.