I would suggest little and often: set up a time schedule for yourself to review perhaps one chapter per day, or one topic, and spend 30-40 mins per day on familiarising yourself with the material. The brain benefits greatly from exercise and training, and it seems that your text books are well set up to help you with this as you can utilize the quizzes and powerpoints in your sessions.

If you learn best by hearing information (auditory learner), you might want to find out who else is taking these classes and talk to the other students about organizing a study group. If you can read the textbook selections to each other, discuss and analyze the lab problems and procedures together, talk your way through the difficult spots in the materials, all that auditory involvement should help.

Getting the books is a good first step.  I also suggest pre-reading the table of contents for each.  This will give you an idea of what the course entails.  Do a little inventory to see how much prior knowledge you have in each course.  If possible, get the syllabus for the classes so you can see which parts of the texts are used and where the focus is.  I suggest reading the first chapter in each book, because it will give you an overview.

Your genetics book has a companion website that will help you to study more effectively. Go to this link:

http://highered.mcgraw-hill.com/sites/007352526x/student_view0/index.html

On the left side of the page there is a drop down menu that will let your choose a chapter from the book. There are practice quizzes, powerpoints for each chapter, and many other resources available there to help you. These materials can be used to prestudy and also to review and test your understanding of concepts.

For the chemistry class, the website is:

http://college.cengage.com/chemistry/general/zumdahl/chemistry/6e/students/index.html

For this site, the chapter overviews would be a good place to start.

This is an excellent way to prepare for your classes. Your first step should be reading the first few chapters of textbooks in order to determine whether you are adequately prepared for the courses. Reviewing your textbooks and notes from your high school chemistry and biology classes is a good way to make sure that you are ready for college level material.

Another thing you might do is start preparing your study materials for the term. Look at the new terms being introduced in the texts, and make flashcards for each term or key concept you do not know. That way, you can have much of the vocabulary and key concepts set in your memory so that you can understand the material more easily and don't need to cram as much for tests.

You can also skim over the main chapters of the books and identify sections that seem particularly difficult and perhaps look for supplementary materials to help you understand them.