Are you seeing your lights flickering?  Do you hear buzzing from your power outlets?  Do you smell something burning?  You don't have Casper playing tricks on you, your home is telling you that you need to call an electrician.  Knowing what signs you should look for can prevent dangerous situations that could lead to either electrocution or fire.  

So what should you look for?
🔥 Burning Smell - If you notice there is a burning smell (and you haven't just turned on your heater for the first time in a long time without dusting it), and it is coming from either a power outlet, light switch or light fitting,  turn the power off at the electrical panel (if you are capable of doing so), and then ring your electrician.  There could be a faulty unit, loose wiring, or power overload somewhere that needs attention.  
🔥 Buzzing sound - should you hear this from your power outlet or light switch you need to contact an electrician.  Loose or aging wiring, or a fault with your device could cause this sound.  Get a professional in to check and make sure things are safe.
🔥 Flickering lights - Have you had a power surge?  Often after a power surge you could get flickering lights.  Check that your bulb has been secured properly, if the connection is not fully there it could be the cause.  If bulbs are secure, and you know they are new, then you should contact your electrician.  Flickering lights could mean you have loose or aging wiring that needs attention.
🔥 Tripping circuit breakers - If you are constantly causing your circuit breaker to trip, and you have gone through the exercise of eliminating your appliances (so you know it is not a faulty appliance) then call your electrician so you can get your load checked.  Overloading is a potential fire hazard.
🔥 Mild shocks - if you have started to receive a mild shock when you touch a plug or switch you should contact your electrician.  Something could be wrong with your wiring.

If you are ringing an electrician for any of the reasons above, be sure to mention it to them so they are aware of the urgency behind the job.