1 Shorten your cables
Cable length affects signal strength. Ensure that the length of cable is as short as possible between antenna and receiver. Also, ensure that the cable is a good quality quad-shielded coaxial cable (RC6), rather than the standard cheap white cable.
2 Check with your neighbours
If your neighbours' reception is as bad as yours, well at least you can club together to complain to whoever will listen. But if you find that some have good reception, you can check out their setup and maybe learn what the trick is to getting good reception in your area. Look in particular for the direction of their antenna, the type of antenna, cabling and even tuner card in their DTV setup for clues.
3 Retune your stations
If you have bad signal, there's always a risk that autotuning your signal will lose half your channels (we know, we've been there!), but stick at it. Especially after making changes to your setup, whether it be antenna, cable or other adjustments, always retune. Remember, too, to retune each time a new station is added to the lineup - it's worth a fresh scan every few months.
4 What about your antenna?
If you are still using an older analog antenna, you may need to update to an antenna that performs better with digital television. A way to tell whether you should update is to check signal strength of channels 6, 8, 10 and 11. If channels 10/11 are much worse than 6/8, then a new antenna is worth looking into.
5 Ask an expert
If you live in a shared house, there may not be much you can do to the existing setup - especially if you are renting. But if you're in a strata or house, it may be worth calling in an expert. Antenna and TV signal technicians can advise on your antenna type and strength, suggest solutions and tune your TV to different masts than you currently use.