Here is a study tip for all you science students.
Go to the library and find all the textbooks you can on your given subject - especially for Organic Chemistry. Since I am referencing Organic, I will use the subject as an example.
When I was in first semester Organic Chemistry, there was an Emeritus Professor who left the department. He was a great teacher, but more than that, he was a mentor and a friend to many of the undergraduate students. When he left, his office still had all of his books in it and come to find out, he left all the books to the department.
There were only a handful of students who went to collect books and see if we wanted any of them. I found a page labeled with the semester, year and exam number next to a problem. That gave me the idea that there are books with old exam questions.
So, I not only took all the books that I could to practice the problems from, I went to the library and used the problems from those textbooks to practice.
Science at an undergraduate level is about practicing different problems over and over again.
Here is a practice problem from Fessenden and Fessenden Organic Chemistry 5th Edition:
"Draw Newman projections for the anti and gauche conformations of (a) 1-bromo-2-chloroethane, and (b) 3-hydroxypropanoic acid, HOCH2CH2CO2H."