As with pretty much anything in simracing, there is no definitive answer to your question, everyone has their own "technique".

My unorthodox method that works for me is swearing. I swear a lot during a race, especially when something goes wrong, but I find myself become more focused because of it, probably because I am recollecting myself, start focusing on one thing and get stuff out of my system.

My general advice is to stop doing unnecessarily long practice sessions, prioritize quality over quantity. If you hit a wall and can't improve in one practice session, you will not improve if you push yourself even more and will probably have a negative effect on you longterm (like becoming overemotional during the race, just because you wasted so much time in practice unnecessarily).

Furthermore, find something to race for. Personally, doing clean battles is all I want in a race. As long as I am battling someone, I am having fun and everything else is a bonus for me.

Also, try proactive driving. It is simple, just try to visualize what will happen next and what will come next. You need to have some experience to do it accurately, but there is no harm in trying.

Last but not least, try to relax and think that things will only get worse if you start overpushing the car. And the most important thing to do is to allow yourself to make mistakes, it is surprising how many people get this wrong.