(from The Tibetan Book of Living and Dyingby Sogyal Rinpoche)
Invoke in the sky in front of you the presence of whichever enlightened being inspires you the most, and consider that this being is the embodiment of all the buddhas, bodhisatvas, and masters. Even if you cannot imagine in your mind's eye any one form, just feel the presence strongly and invoke his or her infinite power, compassion, and blessing.
Open your heart and invoke him or her with all the pain and suffering you feel. If you feel like crying, don't hold back: let your tears flow, and really ask for help. Know that there is someone who is absolutely there for you, someone who listens to you, who understands you with love and compassion, without ever judging you: an ultimate friend. Call to him or her from the depths of your pain, using the mantra OM AH HUM VAJRA GURU PADMA SIDDHI HUM, the mantra that has been used for centuries by hundreds of thousands of beings as a healing spring of purification and protection.
Imagine and know now that the buddha you are crying out to responds, with all his or her love, compassion, wisdom, and power. Tremendous rays of light stream out toward you from him or her. Imagine that light as nectar, filling your heart up completely, and transforming your suffering into bliss.
One way in which Padmasambhava appears is simply sitting in meditation posture, wrapped in his gown and robes, exuding an enchanting feeling of warm and cozy comfort, and with a loving smile on his face. In this emanation he is called "Great Bliss." His hands lie relaxed in his lap, cradling a cup made from the top of a skull. It is full of the nectar of Great Bliss, swirling and sparkling, the source of all healing. He sits serenely on a lotus blossom, ringed by a shimmering sphere of light.
Think of him as infinitely warm and loving, a sun of bliss, comfort, peace, and healing. Open your heart, let out all your suffering; cry out for help. And say his mantra: OM AH HUM VAJRA GURU PADMA SIDDHI HUM.
Imagine now thousands of rays of light streaming out of his body or from his heart. Imagine that the nectar of Great Bliss pours down over you in a continuous stream of soothing, golden liquid light. It flows into your heart, filling it and transforming your suffering into bliss.