So you want to know how to begin creating a plushie cow?

Your very first decision is choosing a plush fabric. Is it printed or is it solid black and solid white? Printed spots will result in less sewing and randomly placed spots. Solid colors require more sewn parts to create the cow and results in every cow pretty much looking identicle. Either choice is fine. The effect on your cow is obvious. 

See here. The cow on the right has printed spots. Every cow will be a little different. The left cow uses sewn patterns to create consistency. This may be a better choice if you are trying to create a specific cow from a storybook for example.

How about body style? Do you want him to sit like a traditional teddy bear as seen above? Or is a somewhat more natural position what you would prefer?

There are lots of ways to create a nose and hooves. Length of plush influences the design as well.

Again, printed plush that is very short... maybe 2mm. And solid colors that are more like 5-6mm long.

Start sketching. It's fun to see what you can create.