To mark the Shivratri festival, devotees wake up early and take a ritual bath. After wearing clean clothes devotees visit the nearest Shiva temple to give ritual bath to the Shiva Lingum with milk, honey, water etc. On Shivaratri, worship of Lord Shiva continues all through the day and night. Every three hours priests perform ritual pooja of Shivalingam by bathing it with milk, yoghurt, honey, ghee, sugar and water amidst the chanting of “Om Namah Shivaya’ and ringing of temple bells. Nightlong vigil or jaagran is also observed in Shiva temples where large number of devotees spend the night singing hymns and devotional songs in praise of Lord Shiva. It is only on the following morning that devotee break their fast by partaking prasad offered to the deity.
During Samudra Manthan by the gods and demons, a highly toxic poison came out of the ocean. As per the advice of Lord Vishnu, gods approached Lord Shiva and prayed him to protect life by consuming this poison. Pleased with their prayers, out of compassion for living beings, Lord Shiva drank this poison and held it in his throat by binding it with a snake. The throat became blue due to the poison (Thus Lord Shiva is also know as Neelakantha) and Shiva remained unharmed. The wise men advised gods to keep Lord Shiva awake during the night. To keep him awake, the gods took turn performing various dances and playing music. A vigil was thus kept by the gods in contemplation of Shiva. As the day broke out, Shiva, pleased with their devotion blessed them all, and also said that whosoever worshipped & contemplated on him on this day shall be blessed with the fulfillment of his or her wishes. Since then, on this day and night - devotees fast, keep vigil, sing glories of Lord and meditate.
Another favorite is the story of Lubhak. I have seen this depicted in Om Namo Shivaye beautifully and find it rather soothing.
There once lived a tribal named Lubdhak, who was a devotee of Shiva. It was his usual practice to go into the forest to collect firewood. One day he wandered deeper than usual and night fell before he could come out. It was the night before the no moon night and the thin crescent moon offered no light. He was not able to find his way in the dark and soon got lost. A hungry tiger smelt him out and with a loud roar made his intentions clear. Lubdhak knew he could not outrun the tiger and so he climbed up a bel tree. In order to keep awake so that he would not fall down in his sleep he began to pluck the leaves from the bel tree and drop them one by one, each time chanting “Om Namah Shivaya”, which means I bow down to Shiva. In this manner, he passed the night. Until dawn, he had dropped a thousand bel leaves. When he descended the tree in the morning, he saw a lingam, which he had missed in the dark. Unknowingly he had been dropping leaves on the lingam. This was the 14th night of the waxing moon of the month of Phalgun and came to be celebrated at Mahashivratri.
The spiritual significance of Shivratri is also fascinating.
Maha is the Big One, Shiv means auspiciousness, and Ratri means night; this is a day when we awake to the most auspicious truth within ourself. Night stands for darkness i.e. ignorance, in which all beings sleep & then dream. Our present transmigratory existence and limited individuality is nothing but a big dream. Freedom is never by some unique or scintillating experiences in this dreamy realm of existence, but only by waking up to that which is not a product of mind. That which is not a product of mind is the Self, the Atma. Mandukya Upanishad calls that non-relative truth of Self as Shiva. That is referred to as the fourth state of the Self, the Turiya. It is the most auspicious one, knowing which one truly wakes up and gets 'as though' liberated. One who knows the Atma as Brahman alone is a liberated one. The other three states apart from the Turiya are the waking, dream and the deep sleep states - when we turn extrovert and try to get experiences from the things around, revel in our imaginary worlds, or just switch off and rest, respectively. The fact that the special sadhana of this day has been kept for night implies that we need to simulate deep sleep, i.e. no flights of mind as in waking or dream states. Turn away from all experiences, physical or mental and just become quiet. No responsibilities, no desires, no burden to achieve anything, no roles to play, no regrets, no aspirations - just as in deep sleep but all consciously. When all relative roles and their corresponding thoughts are kept aside and the mind is quiet, then that which remains is that which is not a product of our minds - the Shiv tattva, the turiya, the auspicious one. Let us awake to that and realize it to be our real Self, thereafter, let this free and awakened mind respond to any situation around, there will be just the fragrance of auspiciousness in everything. That will be the real celebration of Mahashivrati.
Many thanks to www.mahashivratri.org and www.vmission.org for this knowledge.