Learn to operate a metal detector by first practicing with metal items of different kinds to distinguish the different sounds the detector makes for each type of metal. If the beeps are not distinct enough between valuable metal and other metals, adjust the settings until it works for you.
Practice listening to the way different metals sound by using common objects, such as aluminum can tabs, nails and screws, pennies, gold or platinum rings and coins. Some detectors allow you to input what you are searching for so they don't beep for anything else. Once confident, find a searching pattern that is easy to remember and that works for each terrain you search. A pattern keeps you from covering the same ground twice.
When searching, it is important to know when and where to dig if you detect an object that may hold value. Narrow down the dig site by moving the detector back and forth and then up and down the site until you are able to pinpoint a more specific section. Using a plastic trowel, dig up a small amount of earth, place it in a bucket and then run the detector over the ground again to be sure the object has been lifted. Put any non-valuable items to the side to avoid picking out the same object twice. Objects of value cannot be cleaned or you risk lowering their value; instead, use a soft brush and clean water to remove any loose residue.