Cleaning of Crystals can be done through following ways :-

Salt Water :

This is the most popular way to cleanse crystals. Put your crystals in salt water as the salt water has the tendency to absorb negativity.

Sea Salt :

Crystals can be placed in sea salt for up to 24 hours for cleaning.

Sunlight or Moonlight :

Place crystals under the light of a full moon/sun for 24 hours. The rays of the sun and moon are full of energy.

Smudging :

It's a much quicker way to clear crystals. Pass your crystals several times through the smoke incense like Nag Champa or Gugad.

Reiki :

As a Reiki practitioner just like healing your patients heal your crystals and given them universal life force energy.