Whether you're building new stairs or just renovating, you'll probably want to install a new handrail with any staircase remodeling job. Installing a handrail for your stairs should be done as a general rule wherever there are 4 or more steps. You won't need a lot of previous skills to install a handrail, just some basic hardware, but you do need to pay attention to the first step--measuring.
Mark with a pencil where the top of any existing railing lines up with the wall. Use a level to make sure that the pencil reaches straight across the top of the railing to where you place the mark on the wall.
Measure up from the ground on each step to the desired height if there is no existing handrail on the staircase. Choose a height between 30 inches at the low end and 36 at the high end.
Measure from the same spot on each stair and make a pencil mark on the wall. Use the tape measure to check that the points form a straight line.
Be aware that the height of the handrail marks the height of the top of the handrail, which will extend several inches below where you have marked depending on the size of the railing.
Plan to leave about 3 inches between the rail and the wall when you install the rail.
Consult standard building codes in your area to make sure you install your rail at the appropriate height. Also keep in mind anyone with special mobility needs who will be using the rail--if you are installing a handrail specifically for the use of an elderly person, measure a comfortable height for that individual within the 30- to 36-inch range.