Inappropriate or uninformed cleaning methods can destroy, rather than protect, our heritage - however well meant such activities might be by the individuals undertaking them. The general principle of "less is more" is vital - for example, when cleaning brass you should dust lightly once or twice a year and carefully remove dust trapped in tooling and crevices with a soft bristle brush - brass polishes should NOT be use to shine historic brasses. Similarly, for clear glazing you should use a soft, clean cloth and simple water (with just a few drops added of methylated spirits) rather than applying chemical cleaning products. All materials are subject to ongoing change and cleaning should respect this - the aim should be exert responsible and informed stewardship over metals, woods, glass, textiles and stone, truly caring for the long-term well-being of such materials rather than simply making them shiny or new-looking.
Detailed advice: National Trust Manual of Housekeeping.