If you're going to be doing a significant amount of writing for one or more of your instructors this term, the beginning of the term is the best time to drop by during office hours and speak with them about writing.
Instructors aren't snowed under with grading yet during Week 1. They're interested in getting to know their students. You, as a student, aren't snowed under with coursework yet. You're still interested in buying books.
So: a good five or ten minute conversation about what your instructor hopes for from his or her students' writing can be very efficient and productive at this point in the term. You might ask what writing handbook or style of writing your instructor prefers. You might ask if there are any samples of writing--journals, books, websites, etc.--that your instructor feels are examples of what he or she likes. Maybe your instructor can give you some tips on reading or research you could start on for the first paper you'll write this term.
We are not suggesting being fakely complimentary of your instructor or otherwise brown-nosing in any way. We are simply suggesting an authentic five or ten minute conversation that can help you make some decisions about a handbook to buy, some reading to do, and maybe how to anticipate and schedule your workload over the next few weeks. That's it.
Maybe right now you are saying to yourself, "Dude. Nobody does that." Our response is: You mean almost nobody does that. But a few people do. And they usually do well on their writing assignments, because they know what the instructor is looking for from students.