If the flickering is limited to a single light, ensure the bulb is securely fastened in place. Bulbs can become loose over time and lose their connection to the socket. Tighten the bulb if necessary. If it fails, you might try replacing it.
If turning on your air conditioner or washing machine causes several lights to flicker, blink or dim, your issue might be an overloaded circuit. If the flickering occurs on a regular basis, is intense and/or does not stop immediately, you could have a wiring problem. Make an appointment with an electrician to determine the root of the problem.