I've found gold where it had no business being, but most of the gold I've found has been in areas that were famous, early discovery sites--ones that were extensively worked by the regular miners and by the meticulous Chinese. However, no one, no matter how efficient they were, nor no matter how long they worked an area got all of the gold.
There's always some rock that hasn't been moved, some piece of brush that's discouraged countless others, some sheet of bedrock that hasn't been pried up, some undiscovered higher bench, some virgin strip of ground under hand-stacked cobbles, some trashy area that what too noisy for former nugget shooters to detect, or some newly slumped washed out or caved off area that's waiting to be explored and detected.
The gold is still there; however, there are still new virgin areas waiting to be discovered, but the very fact that they're still waiting to be found lets you know that most of them are in remote, hostile environments as the Oldtimers were very good at prospecting out gold and goldfields.
So, I'd first look in old goldfields that were very rich, then after you find some gold--and you will if you stick with it, branch out from there. As others have suggested, tons of research really does pay off.
Good luck, and all the best,
Lanny