First off, congratulations. Anyone who's not glitching and trying to do it legitimately will always have my respect.
Secondly, I'll just add-on to some of the points that's been made:
- Choose whichever camera view you're comfortable with. Although in chase cam, the car may appear to be somewhat slower as compared to bumper cam, which may help. I used bumper cam as I am always used to it.
- Again choose AT or MT as you're used to. AT will probably be easier, but with MT you have more flexibility.
- You can mess with brake balance, but I find it didn't do much for me. So left it as default.
- From easiest to hardest would be Monza -> Nurburgring -> Suzuka, although quite a few ppl felt Suzuka was easier than Nurburgring. Or you can try the killer way - master Suzuka first, then Nurburg and Monza would be a piece of cake.
- Try experimenting with different ABS settings. When I went from ABS 1 to ABS 10 in Nurburg, I found new ways of turning/braking, it's like I had an epiphany. I then went back to ABS 1 and kept on improving my times from there.
- After the 1st lap, if you feel you're within range of getting gold - turn off the ghost car (press Up on the D-pad) so that you don't get distracted when you're near him.
- In fact you may want to turn off all Race Info Display altogether (pause during race and goto Quick Options).
Lastly, are you on a wheel or DS3? Didn't see this mentioned yet.