When I'm working with real race drivers in simulators, the first thing we get them to do is just drive around slowly like its a Sunday afternoon drive. But, importantly drive the correct racing lines, and talk to yourself about braking points etc. Then you speed up in slow increments. You'll feel slow but you'll be doing all the right things, and it'll feel comfortable. At the point where you speed up so much that you feel uncomfortable stop, sit for 5 or 10 minutes and think about what you are doing. Then work on 1 or 2 different areas of the track at a time, and give yourself time in between to think about what went right and what went wrong, so you can bank a plan of action for the next lap of something to try.
I worked with an Indycar driver for a few real tests some years ago, and he would drive around about 0.5 second off a really good lap to give himself time to fully analyse what was happening each corner. Then when we wanted a real fast lap, he'd say don't ask me for feedback because at that point he'd be fully focused and commited and had no capacity for anything addiitonal.
Last thing, look further down the track. So many people are guilty of looking too short and then you don't have so much time to react and position the car in the right place etc. It's really hard to change but it does make a big difference.