Veerle, a web/graphic designer living in Belgium, created this three-page pen tool exercise back in 2007. She writes about it on her blog here: https://veerle.duoh.com/design/illustrator-pen-tool-exercises
This video is an example of me completing the exercise and giving tips as I go.
Good luck! Practice. Practice. Repeat. Practice.
Remember, as Veerle writes, “Once you have done these exercises several times I hope you’ll understand the Pen tool and its quirks a little better.”
Download this exercise from DropBox here: https://www.dropbox.com/s/5gmjm3vw9jl8dfm/Pentool-exercise.ai.zip?dl=0