You must study regularly and intensively. Organic chemistry is both detailed and extensive. Study each chapter before as well as after it is discussed in lecture. Keep up with the problems. Use the time before exams for review, not for cramming.
Organic chemistry is relentlessly cumulative and intensely interrelated.
Once you fall behind, catching up is very difficult. Your disciplined effort will be repaid by the satisfaction that comes with mastering complex material, and that will result in a grade to be proud of. You will find that much detailed information must be remembered. This is easier and more effective if the details are connected by a framework of general ideas such as mechanistic patterns and functional group similarities. Try to connect each new bit of information to what you already know.