First, make sure both are written as fractions (either proper or improper.) You cannot multiply with mixed numbers easily! After both are changed to fractions, take the first fraction, unchanged, and MULTIPLY by the reciprocal of the second fraction.
Example: 1 and 1/2 divided by 3 and 3/4
Change to 3/2 divided by 15/4
Change to 3/2 times 4/15
Equals 12/30 which reduces to 2/5.
Hope this helps!