Estimate the amount of square footage that needs primer and identify the material that you will paint. To find the square footage of walls, measure the wall's length and height in feet and divide by 12. Use this as the minimum amount of area covered by primer.
Adjust the amount of primer needed based on certain characteristics of the surface. Smooth walls require about a gallon for every 350 sq/ft, while a gallon only covers about 250 square feet of rough textured wall. Account for the current color and the new color. Dark colors need to be covered in several layers of primer, especially when a lighter color replaces it.
Purchase the best quality primer that fits in the budget. Not only does good quality primer have a smoother finish but also it tends to cover better. It sticks to the surface of the object and allows for the paint to bond.
Prepare the walls or other surface by washing it thoroughly. Use a drop of dish soap in warm water, wiping with a rag and allowing it to fully dry.
Apply the primer in long, even strokes, making sure you cover the entire surface. Allow this initial coat of primer to stand for about an hour before painting over it, but check with the manufacturer's directions.
Sand the surface lightly after the primer has dried. This helps to smooth out the surface and give the paint a bonding agent. There's no need for rough grades or much effort, just pick a fine grade of sandpaper and rub lightly over the primer and finish by applying the final paint color.