If possible you should definitely fit a correctly aligned and polarized TV antenna externally, preferably as high as you can. Alternatively if you have an existing outdoor antenna with a co-ax cable leading indoors, you could plug that into a distribution amplifier and then have several cable outputs to various rooms. Amps are easily available from Argos etc. If the catalogue quotes a 'dB gain' figure then go for the highest figure, ie 6dB would be three times more powerfull than a 3dB gain model. Hope this helps.
Steve