Understanding the principles of trail braking is HUGE in this game due to the way the car's handle.
Firstly I recommend to anyone having trouble setting their brake pressure to "low".
Mainly because you will lock up far less and will ease you into a more gentle brake technique without compromising much time/having to use assists.
Just try to remember that you should be full brake into the heavy braking zone initially(think T2 Melbourne), and in straight line zones its as simple as learning to back off the breaks as your speed comes down and as you need to turn in, ideally releasing the brakes only when your car hits the apex. It's generally a sign you were perfect on the brakes and line when your car "feels" like it is going to spin but maintains balance on the turn-in and traction on the exit.
Then when you have issues braking into other corners, take these factors into account.
-Slope(braking uphill you can be harder/later on brakes than downhill)
-Camber(off camber corners are more likely to lock than cambered-in bends where you can carry the speed)
-Braking angle(for example if the braking zone is perfectly straight you can be harder on the brakes)
-Speed of car entering braking zone(generally the slower you are the less brake you need).