Hello I'm an Ayurveda doctor. Getting your mind to concentrate is the first thing to do before you start studying. Get your surroundings favourable neat clean and arranged where you sit to study. Pray and keep photos of God near your study table. Have a bath before you sit to study. Yoga and meditation can be practised a can do wonders in your concentration and learning ability. Avoid all co curricular activities at least 3 months before your exam starts. You may take 5 gm to 10 gm of Brahmi ghritha before bed and 1 tab manasamitra vatakam. Thank you. Good luck.