The best grasses for shady areas include fescue in the north and zoysia in the south. Even grass that grows in shady spots needs between 3 and 4 hours of sunlight per day.
Once shade-resistant grass is planted, it should be watered every day until it grows to be at least 2 inches long, or long enough to mow. Once it reaches that length, it can be watered on a regular watering schedule like the rest of the grass on the property.
If the grass does not receive enough sunlight due to large trees, try pruning the trees back a bit to allow more light to penetrate the area. Using a good starter food as fertilizer will allow the grass to grow healthily.