Print a list of subtraction and addition problems. This will allow you to check off each problem you write to avoid missing one or writing one twice.
Prepare index cards or cut out cards from paper, preferably from thick or heavy duty paper such as card stock, poster board or thin cardboard. All cards should be the same size. Lay the stack down on your working surface.
Write a math problem on one side of the card and then flip over the card and write the answer. Repeat this process for each card. Begin with addition or subtraction and work down the list in order until you have written them all. For example, begin with 1 + 0 or 1 + 1 for addition, or 1 - 0 for subtraction.
Check off each card you write from the list. Make sure you are writing the question and answer both right side up and make sure the marker is not bleeding through the other side, giving away the answer.
Laminate the completed flash cards to help them hold up after multiple uses.