Problem with using logic in programming languages. How can I overcome this deficiency?

java programming

dear experts ,
i m not able to understand what type of logic i have to apply when and why in programs .it is a problem for me because this time i have my icse board exams and our programming is of 60 marks and i want to score high and i may lose marks in my java programming.so please try to reply me to get me off from this problem.
thanking u,
vaishali solanki