In
subtraction the denominator must be the same.

You
subtract the numerator (the top number).
Never
subtract the denominators (the bottom number). 
When
you borrow for subtraction, remember to reduce the whole number by one
and add the denominator to the numerator giving you a new numerator quantity.
Therefore
4 1/4 becomes 3 5/4. 
Always
reduce your answer to its lower terms. Remember to move the whole number
then reduce the fraction (4 4/8 = 4 1/2) it sometimes helps to place
the reducing number between equal lines.

You
may want to use the Magic Numbers 2, 3, 5, 7, 11 