GT5 is hard to drive...really

The only way to get better is to be professional, ie, practice proper driving styles.
I also think there's some sort of brain barriers one needs to cross with high speed racing games, as I think there's so much info or unnatural info the brain has to register within such a short timeframe, that it takes a lot of practice to condition your eyes to dealing with such speeds....but that aside.
1...respect the racing line
2...be smooth and precise on change of direction{noob killer}
3...develop braking markers
4...be careful on both brakes and throttle, and don't overdrive the car thru corners, let it unwind and as soon as you feel the chassis loosen up, flatten it!!!
5....
protect yourself with heavy wing values and slowly decrease them as you improve
6...pay attention to the car behaviour, ie, understeer, oversteer and braking.....and modify your set up or driving style to produce a cleaner lap.
7....practice, but don't just drive a dog around, if the car is poorly set up, modify it accordingly.