I tried a bit of a new process with these guys.
First I laid in some tonal values with markers. I was concerned with trying to get forms to read one in front of the other as well as creating depth with atmospheric value (Darker in front/lighter in back)
Then I took a pen and added more finite shapes and details. And Lastly went over them again with another pass of value markers.
Not sure if this is the best way to work for me, but it was a blast to try!