Raceboy77, who's one of the fastest Forza drivers out there, made this video with some tips on how to brake:
I particularly like the fact that he talks about how hard you should brake (60-80%) and pulls up the telemetry to show it, it's something I'll be practicing. While he does do a bit of trail braking (e.g. around the last turn at Sebring), he mostly doesn't, I had a short chat with him about that when he stopped by the Forza Twitch channel yesterday. Mainly I'll have to make sure I brake consistently hard enough, have noticed I get outbraked every now and then.