My advice for DR is simple, get quick and learn how to race offensively and defensively.
You will reach a level to which you won’t improve, so my advice would then be get quicker.
Don’t heap pressure on yourself for DR, if your looking after SR by racing cleanly, but at your fastest DR will look after itself.
There are ways to get faster, get friends in your friends list and run the circuit experiences over and over until your top of your friends list, or you’ve squeezed every last tenth and theres no more to be had.
Watch the quick guys youtube videos, study their lines and apply then to yourself.
But it’s simple,
The least time on the brakes.
The most time on the Accelerator.
The fastest line from A to B.
The least amount of steering inputs.
The highest cornering speed.
Plan your overtakes.
Plan your defenses.
Learn the chess of racecraft.