These one line drawings are so much fun and they only take a couple of minutes.
The idea is to leave your pencil on the paper at all times roaming in and out of the subject. Don’t stress about being accurate, just let go and describe the different angles and curves in an arbitrary and spontaneous way. This is somewhat similar to gesture drawing, the only difference being that the drawings are done in one continuous line.
Remember, this is not an outline drawing. People, pets, plants or furniture all make good scribbly one line drawings.
This type of drawing is great for warming up before drawing from the model.