Consider the appliance cover to be rather like a soft-sided box, with somewhat rounded top corners. If you can provide the dimensions of this "box", we can sew it for you.
First, choose your fabrics: one for the outside of the cover, one for the inside, and one for the trim (this can be the same as the lining color, if you wish). Please note that there is only trim on the outside of the cover, not on the inside.
Next, measure the height (top to bottom) of your appliance, as well as the width (side to side) and depth (front to back). Please measure to the nearest 1/4 inch. Do not add on for "ease"; we will increase the dimensions you provide by 1/4" to 1/2" to give a bit of "roominess".
If you are measuring for a mixer cover, steamer, or crockpot, please also measure the circumference (all the way around the appliance at the largest point). This will allow for a better fit. If you plan on storing the bowl(s) together with your mixer, do your measuring with the bowls in place.
Please do turn your appliance around to check for any handles, plugs, etc. which need to be taken into account when measuring.
Remember to measure carefully! Your cover is being custom-made for you, and as such, is not returnable.