Here is a merkaba meditation using a crystal merkaba as the focal point to help your consciousness to enter the meditative state.
Holding the crystal merkaba in your hands, close your eyes and take deep breaths, concentrating of each breath, feeling the in-breath and feeling the out-breath, feel the way your breath becomes calm and allows you to go within. Centre you consciousness in you heart, just allowing yourself to relax and be still.
Now take your consciousness into the crystal merkaba held in your hands, visualize yourself sitting within the crystal merkaba, and feel its energy around you. Feel the loving protecting energy surrounding your Being. Know that you can enter this state of consciousness at any time, it is a place of safety and love.
Stay relaxed and remain within the crystal merkaba energy for a while. When you are ready, slowly bring your consciousness back to the room you are in, concentrating on your in-breath and out-breath to help bring you out of the meditation, then open your eyes to become fully present once more.