A general rule for any type of textile imprinting is to use more contrast than you might otherwise. Make sure you've got enough contrast between these colors. Simple designs often do the best, resulting in a nice professional looking pad. However, don't forget to include your phone number or web address. Remember, mousepads have rounded corners, so trying to print a square border around of the edge of the pad simply does not work.
Alignment is a problem and it just looks plain awkward.
Along the same lines, do not place important text, phone numbers, etc., too close to the edge of the pad. Especially in the corners. Mousepad size, proportions, file formats and related info can be found here . It's always a good idea to send a color print of your design if possible. An important note about color.