Draw the basic geometric shapes for an outline of your cat. These are your guidelines which you'll erase later. Because you want to show an arched back, your cat will have to be standing. Draw a circle for the head and add an oblong behind for the body. Draw two short rectangles for legs with smaller circles for paws at the bottom. Add a smaller oblong circle standing upright for the tail.
Give your cat an arched back by changing the oblong shaped body so that it arches upward. Do this by adding height to the top of the oblong and curving it in from the bottom. Think of an upside-down "u" or drawing a mouth upside down. You want to show the arching -- a cat has to pull it's long body inward, creating that upside-down "u" shape. This elongates the legs and shortens the length of the cat's body as well.
Add the features for your arched back cat. Draw a light cross over the face to use as a guideline for placing the cat's facial features. Put the eyes on either side of the cross at top, add the nose where the cross intersects and the mouth below the nose. Mark a spot for each ear at the top of the head and then add a triangle centered over the mark. Follow the rectangles and circles for the legs and paws to draw the legs. Taper the legs, making them wider at the top and thinner at the bottom.
Sketch the details for your cat. Add slits to the eyes which run up and down in the middle of the eye. Put dots where the whiskers start and add whiskers. Give sharp teeth to his mouth and add claws to his paws. Add spikes to the hair on his back and make his tail bushy, if he's a scared cat.
Erase all of your guideline geometric shapes which helped you to lay out the basic form of your cat. Then, paint or use crayons, markers or colored pencils to finish off your cat. You can also add other things to your picture like a crescent moon, if it's a Halloween picture; another cat; or a mouse in front of it.