In a month preparing for board exams and to score good is a really tough job indeed. Though I am trying to help you.
First read the textbooks of your subjects thoroughly within a week. do not go for too many books rather stick to one authentic text book of a particular subject. It will save your time.
Study the previous papers of each subject which will provide you an idea about the question pattern. now practise them by writing the answers in your own hand in a stipulated time period, like any mock exam. if possible correct the answer scripts with your teachers. It will help you a lot.
for important mathematical formulas, write them on a chart paper and stick it on your wall where you can see it everyday, which will help you to memorise it.
For the diagrams of science and other subjects try to draw them perfectly by free hand drawing. If possible try to practise at least 5 diagrams daily with proper pointing.
and most important do not panic, try to keep yourself stress free. Eat healthy and light foods, not so much spicy food. Drink plenty of water, do free hand exercise or a walk either in evening or morning and at least 8 hours of a sleep is must. Best of Luck for your coming board exams.