Provide the energy for the plates to make contact. One analogy is to think of opening a new jar of pickles when the lid is stuck. Supply the energy to move the lid and relax as soon as you feel the lid pop free. Practice this at many dynamic levels and with varying amounts of energy. Listen to, and feel the cymbals move together.
All cymbals react differently when they are struck together.
Depending on the instruments you are holding, it may be necessary to allow the cymbal edges to touch for a longer or shorter amount of time to achieve a full bodied crash. The music will determine the length, volume, and attack of the crash. Follow through, larger arm motions, and top versus bottom edged crashes can be discussed once control over the basic cymbal movement and sound is achieved. These exercises are a first step in developing an understanding of the many sounds and colors that are available with the crash cymbals.