Today, I couldn't make a f***** decent sketch (I wonder if it's only today...), until a moment when my hand got released. BUT, I made a few cat observations, and I prefer to show only those.
No 1: Cats are animals, so...
No 2: They have oval shaped pupils (wow!)
No 3: Their head consists approximately of two basic shapes: a sphere and a box
No 4: (more like a practical guideline) The head blends seamlessly along a curve with the spine.
Next observations: feet shapes