I found the easiest designs to start with were shapes that I was so used to drawing or writing that I did not need to think about what I was doing- loop de loops are like writing "e's" and "l's". Also shapes that we have doodled since we were children like little hearts and flowers seemed very easy. Stippling requires more thought so it was harder
Sometimes your hands speed up on the end of curves which will give you lashes so will need to think a bit about your speed there.
I started with little fat quarter sandwiches and found them a very comfortable size to practice on. I still keep some beside my machine to warm up on.
I found that following planned lines was very hard at first so I decided to just doodle. It was fun, I relaxed and I improved faster then.
Listen to info from lots of people. We are all different so not everything that one person swears by will work for you.