We study the standardized candle method for type II "plateau" supernovae by means of BVRI photometry and optical spectroscopy. An analytical procedure was implemented in order to model the light curves, color curves, and expansion-velocity curves. We find that their V-I colors can be use as proxies of the extinction caused by interstellar dust in their host galaxies. After the necessary corrections to photometry, we are able to recover the correlation between luminosity and expansion velocity previously reported in the literature for this supernova type. Given this and assuming the standard extinction law, our Hubble diagrams show dispersions of 0.4 magnitudes in the BVI filter bands. On the other hand, if the extinction law is entered as a free parameter, we derive final dispersions of 0.3 magnitudes, which implies that this kind of supernova delivers distances as precise as 12%. The resulting extinction law suggests a different interstellar medium in their host galaxies than that of our Galaxy. Calibrating the correlation between luminosity and expansion velocity, we obtain a Hubble constant of 70 km/s/Mpc, in good agreement with modern measurements.