Has your wifi router been dropping the internet connection or is it only that your wifi device has a weak signal and can't connect to the router? Two different problems.
Do you have a computer connected by cable to the router? Does it lose internet at the same time as wifi device?
How many bars of signal strength does your wifi device get? How far is the wifi device from the router?
Does it detect other networks in your neighbourhood? They could interfere with yours.
This has been prepared by TPG: