How should I get grease off of my keyboard?

How to clean your Apple products - How to clean your Apple products - Apple Support

"Using a 70 percent isopropyl 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 bleach. 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."

Wipe gently with a clean dry microfiber cloth. Unless the grease is water soluble, a dampened cloth is not going to enhance cleaning.

But the question is how did the grease get there? If it's just finger oils, the above is correct. If you managed to spill liquified grease or oil on the keyboard, that can mean internal damage to at least some degree.

Just wipe it off gently. Tissue paper or even toilet paper should work.