All the replies telling you to practice for the situation, but its too vague. The best way to be prepared for the almost anything mentally is to be aware.It only comes through meditation. You need to be aware of your surroundings and yourself. You can think straight if you teach yourself. Sit in a room without any sound or anything. Close your eyes and let thoughts comes to mind , but don’t dwleve into each of them let them breeze through. It’s very hard , but you need to practice a lot… Your brain will learn this and you will be aware