Well, there is no set way of becoming a good student or straight A student. We can certainly list and discuss some characteristics of a good student or some study practices or tactics that can help someone achieve good grades. However, it all depends on student's capabilities, skills and motivation to carry these out. Some key characteristics of good students are obedience, sincerity, discipline, motivation, perseverance, leadership and initiative. Good students are generally sincere and motivated in their efforts, follow the rules and instructions of their teachers, take initiatives and help others. Interestingly, many of these same characteristics are required to achieve good grades. For example, motivation, perseverance and hard work are key to good grades. Practice is necessary and there is no substitute to hard work. I always suggest practice, especially for mathematics and science courses, and regular study of all subjects to students. Mock tests and practice sessions also help eliminate the pressure many students feel during examination. Regular study and sincere efforts in homework assignment and quizzes also help.
Hope this helps.