To know how much improvement is possible, you first need to know how much maximum range you can get from your location. Determine your physically possible Maximum Range using the method given in First Post of the following thread:
What is the Maximum Range I can Get?
Once you know what you can achieve, you can find methods to improve range. These include:
(1) Change antenna location and height so that it has an unobstructed view of horizon in most directions. If you cannot install antenna outdoors, try to locate it next to a large window or in attic.
(2) Use a better antenna
(3) Reduce cable attenuation by minimizing length of coax between antenna & DVB-T. The coax attenuation depends on type and length of coax. Up to about 10 meters of coax is ok when used with Pro Stick or Pro Stick Plus, as these have built-in amplifier, but even with these, reducing coax length improves max range / plane count.
(4) If RF noise is too strong, use Filter. The RF noise is caused by other strong communication signals such as Cell Phone signals.