uni of st andrews (i need help)

hi , i'm currently a year 12 student about to go into year 13. i'm well into considering unis now and i know i want to do psychology and st andrew's is definitely gonna be on my list to apply to as their psychology course is known to be amazing. My grades have not been anything special this past year however that is due to a lack of effort which i'm prepared to fix this next coming year. i know the acceptance rate for st andrews to study psych is already like 5.6% so im basically just asking for any advice that increases my chances of getting in. i'm a basic british student, middle class , with no private school education however i do attend a top college if that even counts for anything. basically just want someone to tell me exactly what i need to do to increase my chances of getting in or even if i have a chance to be honest. help is appreciated thankyou :)