It always seems to me that everyone knows all the good roads around them... when I go an see a friend, I research my route there, so that I can gen an idea of the local geography; have a look on forums and generally on the internet to see what good 'driving' roads there are out there.
This may seem cumbersome, and even a waste of time, but honestly, it has lead me to some great roads! This may seem obvious, but I live on the Isle of Wight. If you zoom out in Google Maps, all you see is 3 A roads, but there's so much more than that! There are roads that you wouldn't consider going down that are the best fun, full of great corners, epic straights, and everything in between!
My favourite way of finding driving roads is to just drive! I have a glance at a map before heading out and just driving! A left turn here, a right turn there, straight across that roundabout and so on. Living on the Isle of Wight, everyone knows that there are a few dedicated driving roads; the Military Road along the South-West coast - some good corners, plenty of overtaking spots, and long enough to use a lot of your car's power! More recently though, I have discovered a small road, used by almost nobody that runs almost parallel to the great Military Road, full of complex, tight corners. It's mostly single track, which keeps you thinking on your toes just a bit! There are plenty of open expanses, where you can see enough to put your foot down. Below is a video of these roads. It has been sped up to 4x speed, so sounds like I'm driving a chainsaw... but you'll get the idea. I learnt of these roads not by using a map, but by exploring.
B-Road Drive - Isle of Wight
Things to take from this:
1) I'm not a racing driver
2) My car sounds like a chainsaw
3) You can find some amazing roads, quite by accident!