I need help paying my property taxes

I need help paying my property taxes. I read in the National Taxpayers Union over 60% of properties in the United States are over-assessed. If this is the case how would I know that I've been over-assessed and does this mean I might get a possible 60% reduction in taxes? Its all very confusing to me! Is there anyone who could explain the tax appeal process and how to spot tax bill mistakes. If I can avoid paying 60% of my taxes I would be in a better position financially.