The day
Take a single meal on the Trayodashi. On Shivaratri bathe early, with sesame in the water, and make the sankalpa to keep the fast and worship Shiva through the night. The fast may be without food, with fruit and milk, or one meal of fasting food.
The four prahars
The night is divided into four watches. In each, bathe the linga (abhisheka) and worship it. Tradition gives each prahar its own bath: milk in the first, curd in the second, ghee in the third and honey in the fourth, with water between, though many use all of them each time. After each abhisheka, apply sandal and bhasma, offer bilva leaves (three-leafed, with the smooth side down), datura, white flowers, akshata, incense, a lamp, fruit and sweets, and chant Om Namah Shivaya.
At Nishita, around midnight, perform the most elaborate worship. Recite the Shiva Panchakshara Stotram or the Rudrashtakam, read the Shivaratri katha of the hunter and the bilva tree, and stay awake singing bhajans until dawn.
Parana
Break the fast the next morning, after bathing and a short worship, between sunrise and the end of the Chaturdashi tithi. Give food to the needy before eating.
In a temple
Those who cannot worship at home through the night go to a Shiva temple, where the four prahar pujas are performed by the priests. Devotees queue to pour water and milk on the linga, offer bilva leaves and chant Om Namah Shivaya through the night.