Choose age-appropriate objects. Avoid manipulatives with small pieces when working with very young children.
Select the proper manipulative for the subject. Don't attempt to teach addition using geoboards (boards used to teach geometry). Counters, place-value mats, money and fraction strips work well when teaching addition.
Allow students time to play with the manipulatives in an unstructured way before the lesson begins. Let the children learn the names of the objects, become comfortable with the rules for using the objects and understand what the objects can and cannot do.
Employ different manipulatives to teach the same concept. Teach addition using both an abacus and a set of counters, for example.
Relate addition to the real world. Introduce objects such as coins and dollars to help students understand how to use addition outside the classroom.