You can use a slightly damp cloth. See the following from How to clean your Apple products - Apple Support
Handle your iPad with care to maintain its appearance. If you're concerned about scratching or abrasion, you can use one of the many cases sold separately. To clean iPad, unplug all cables and turn off iPad (press and hold the Sleep/Wake button, and then slide the onscreen slider). Use a soft, slightly damp, lint-free cloth. Avoid getting moisture in openings. Don't use window cleaners, household cleaners, compressed air, aerosol sprays, solvents, ammonia, abrasives, or cleaners containing hydrogen peroxide to clean iPad. iPad has an oleophobic coating on the screen; simply wipe iPad's screen with a soft, lint-free cloth to remove oil left by your hands. The ability of this coating to repel oil will diminish over time with normal usage, and rubbing the screen with an abrasive material will further diminish its effect and might scratch your screen.
Also see the following from that same support article:
Is it OK to use a disinfectant on my Apple product?
Using a 70 percent isopropyl alcohol wipe, 75 percent ethyl alcohol wipe, or Clorox Disinfecting Wipes, you may gently wipe the hard, nonporous surfaces of your Apple product, such as the display, keyboard, or other exterior surfaces. Don't use products containing bleach or hydrogen peroxide. Avoid getting moisture in any opening, and don't submerge your Apple product in any cleaning agents. Don't use on fabric or leather surfaces.
