I’m not saying I’m perfect at being the lead car, but here is what helps me
The more comfortable I am with a track/car, the easier it is for me to deal with a car in close pursuit. Some of this is seat time and practice, but its also important to have a stable setup (over a fast but unstable setup).
I try to check mirrors habitually twice per corner or corner complex: just before and into braking zone, and during or just after track out. Depending on what I see during track out I may watch mirror a bit during the straight. This way I get a read on people possibly overtaking in braking, and a read coming out of the corner. But I’m not “driving in my mirror” which to me leads to mistakes. I try to follow a similar pattern in real life track events.
Some sim-related things
-I use the virtual mirror, and I’ve reduced its FOV so the appearance of distance is more accurate/useful for me.
-triples or VR gives you the ability to check your left-right. My son uses a single monitor but she is proficient using buttons on the wheel to look left-right.
-the Racelabs overlay has a radar tool that can be very helpful.
Regarding braking: I think iracing’s simulation of brakes is fairly rudimentary. I just adjust pad and brake bias to my liking and have not seen an issue. rFactor had a far more sophisticated modeling and I remember having brake failure more than once when I got it wrong.