Try practicing drawing some cubes and cylinders on their own to warm up. Before twisting and turning cubes get comfortable with normal cubes. Just don't lose your mind on it. As for the exercise, don't overlook it, dont rush, try your best ability to do each. In digital it's easy to undo and retry - this leads to fast iteration and making better lines. If your lines are all wobbly, you'll have a wobbly result. If you want it clean, take your time and make each line with effort.
You can also play with what colors you use and lower opacity of the image layer
cheers
