Always use a qualified antenna technician to install and maintain your antenna system. If you are in an area where the signal strength is low, you may need a high-gain aerial for the best reception. Again, a qualified antenna technician can take exact signal level measurements and advise you accordingly.
Your digital TV antenna should ideally be mounted outside on your roof and as high up as possible. It must be pointing in the right direction towards the best local transmitter. The antenna, cables and connections need to be maintained in good conditions - cables and connections in particular can easily become corroded, especially if you live near the sea.
For best performance, a maintenance check should be scheduled at least every five years.