To start with there are a handful of reasons for flickering lights. Let's first establish if it is limited to one room, two rooms or the whole house. The reason for wanting to know this is to narrow the areas in which we will be looking. If it's the whole house it could be your ESP (Electrical Service Provider) and from making a call to their repair department you might save yourself a service call from your favorite licensed electrician.
Once this is ruled out we can begin the process of eliminating items on the list. Remember to turn all power off to any light fixtures and electrical boxes before performing any work. For starters if the lights are flickering in only one room we can check the connection at the light fixture and at the switch. After which we can turn power back on and look for some flickering. Keep in mind that there are times that the problem may arise only after the lights have been on for a while. If we still have some flickering we can assume that the problem lies somewhere between were the switch is and circuit breaker, which brings up a point that we have been looking on one end of the problem and that at this point we could change gears temporally to look at the circuit breaker as a possible culprit.
When examining the circuit breaker be sure to turn all the power off feeding that electrical panel. Ensuring the power is off before inspecting the possible causes of the flickering lights is one of the safety procedures we will always be stressing. After removing the circuit breaker, inspect both the panel and the breaker for signs of heat buildup or arching, which will show up as pitting and corrosion where the breaker attaches to the panel or the busing on the panel. If these check out the problem could still be inside the circuit breaker itself which does not lend itself to internal inspection. At this point you can have it replaced and eliminate it from possible causes. While we are in the electrical panel, we should also be looking at the neutral wire for that circuit. A loose neutral wire can be just as damaging to the integrity of an electrical circuit as the hot wire. After checking the tightness of the screw holding down the wire, give it a little tug to be sure.
To recap, we started at the light in question inspecting the switch box and the junction box that the light is attached to. Everything seemed to be in order so we attacked the other end of the associated problem. After not finding any signs of what could be causing the problem the next areas of interest are from above or below. From here, the real dirty work is ahead of us. Now would be a good time to think about calling in an electrician if you are not up to crawling under the house or in the attic. This is where we attempt to trace the path in which the wire travels from the panel to the light fixture, all of which could entail a number of points in between.
Most houses that have not had any remodeling done would have one of two types of wiring, romex or conduit. If the house is really dated, it would be wired with Knob and Tube. After the circuit leaves the panel it more than likely will either go to a switch box or ceiling box with a light fixture attached. On occasions, in the older homes there may be a junction where the circuit branches out from there. This makes it somewhat easier to trace since we do not have to pull out switches or remove light fixtures. Remember that the most important aspect is safety and that you should always have the power off when inspecting the wiring. If you cannot diagnose the issue, you should consider getting outside help.
