What can an ordinary citizen do to combat Money Laundering?

If you're not the prospective launderer, in fact there's not much you're expected to do. All the job is done by the responsible institutions for you. If you don't intend to "clean" money you received in some illegal way, you don't need to take any particular steps. As the other replier says, as an additional security measure, avoid any suspicious money remittance points, so you won't be disturbed as a potential witness. However, keep in mind that you may get involved as unconscious money launderer e.g. by accepting fake job offers providing you with a premium for receiving money orders and wire transfers and send them further (usually abroad). Any job that is based on using your personal account to transfer money of unknown origin is in most cases bound to ML "industry".