Apple’s free guide book called the iPad User Guide states under Using and Cleaning iPad. "… If you are concerned about scratching or abrasion, you can use one of the many cases sold separately. To clean iPad, … Don’t use window cleaners, household cleaners, aerosol sprays, solvents, alcohol, ammonia, or abrasives to clean iPad. iPad has an oleophobic coating on the screen; simply wipe the iPad screen with a soft, lint-free cloth to remove oil left by your hands."
For additional information about handling your iPad, see the iPad Important Product Information Guide.