Having trouble coming up with something to draw? No worries - while you'll eventually learn how to start from a tiny seed of a thought and gradually nurture it into a complex concept to explore through design and illustration, it's perfectly fine not to be there just yet.
For now though, here's an idea that might interest you.
Everything, a Dragon
The world of dragons and dragon-like things is a vast and varied one. You've got your traditional European ones, with six limbs (four legs, two wings), along with your wyverns (two legs, two wings), and even more as you push east into the more serpentine interpretations.
Take anything - a living creature, a vacuum cleaner, an extension cord, your friend Steve from college - and turn them into a dragon, or a draconic creature of some sort.
Staedtler Pigment Liners
These are what I use when doing these exercises. They usually run somewhere in the middle of the price/quality range, and are often sold in sets of different line weights - remember that for the Drawabox lessons, we only really use the 0.5s, so try and find sets that sell only one size.
Alternatively, if at all possible, going to an art supply store and buying the pens in person is often better because they'll generally sell them individually and allow you to test them out before you buy (to weed out any duds).