Start putting together a gold detector kit. The first item to put in the case should be a small ceramic tile. To use this handy square, turn it over to the back and scratch the nugget in question across. Greenish black streak? You've found fool's gold. Golden yellow streak? You've found real gold.
Put in a magnet - Fool's gold will be attracted to a magnet. When pyrite is heated, it actually turns magnetic. Real gold will show no effect when placed next to a magnet. If you do find pyrite, making a nice magnet out of it is not a bad idea.
Bring a piece of flint - Besides being able to rescue you from a fire less demise if you get lost while mining, flint can also help you decide if it's real gold. Iron pyrite is Greek for "of fire", it is well named, for if you strike a piece of pyrite against flint, you will get a spark. Real gold will produce nothing.
Look for these physical differences; Pyrite will look more pale brassy and be in a crystal form. Real gold will look metallic yellow. It's more often found in nuggets, instead of bunched together like crystals.
After you have tried these methods, you will no longer be another person fooled by pyrite. You will be able to pick out the real gold with ease.