Quality stair lighting increases a home's value, adds to its aesthetic appeal and can improve safety and reduce energy usage. Designing and installing stairway lighting yourself is a straightforward project that you can carry out with relative ease. The complexity of the electrical work is largely up to you.
Design the lighting
Envision the finished product. Determine what kind of lighting you add and where you want it to go. There are many options for lighting, from a simple overhead fixture, to recessed lights, to wall sconces, to theater-style strip lighting, to a chandelier. Check to make sure that you have room to install it and that it can be installed safely. The only other limitation is your budget.
Design the wiring
Those lights will need power. You will need to run the lights on their own loop separate from the primary circuit so that you can control them with switches. Unless your stairway is already wired for this, you will need to install this loop yourself, or contract an electrician to do it. The more difficult option would be to install it behind the wall or ceiling, like the other wires in your house. Alternatively, you can install it in a protective conduit that runs in the nook between ceiling and wall or wall and floor. This option would produce a more conspicuous result, but you will save yourself a lot of work.
First you will need to find a circuit to plug into. Assess how much power your stair lights will use, and verify that the chosen circuit has enough spare capacity to handle the load. If not, you will have to find another one, or install one at the breaker. You may want to hire an electrician for that, unless you are knowledgeable in working on circuit breakers. At the point where you join your lighting loop to the circuit, you will need to cut the circuit and install a simple junction box.
As for the switches, you should use one three-way switch at each end of the staircase. The wiring for this is easy to mix up, so draw a schematic for later reference.
Install the wiring and lights
Once you have decided on what lights you will use, where they will go, where the switches will go and where the wiring will go, it's simply a matter of installation. Your first step, of course, will be to turn off the power to the circuit you'll be working with. After that, install the wiring, the junction box, the switches and finally the lights. Turn on the circuit and test your work.