It’s hard to fold fitted sheets of any size, and crib sheets are no exception. This, however is a fairly simple method:
Using your right hand, drape the corner of the fitted sheet over your fingers on your left hand. Make sure it is inside out.
The short side of the sheet should be hanging down on your left side and the long side directly in front of you.
With your right hand, pick up the next corner on the long side and drape it right side out on top of the corner that is already on your left hand.
Lay your sheet down on your table with the corners still inside one another. Make the other 2 corners look just like your first set of corners with one inside the other.
Smooth out your sheet as much as you can. It should now look like this:
Bring the left side of your sheet over to the right side of your sheet. Smooth and tuck the edges until you have a rectangle.
Bring the bottom of the sheet up to fold into thirds. Remember to pull the sheet tight and smooth out wrinkles as you go.
How to fold your crib mattress pad might also be helpful.