Math, math, math! I'm taking two different chemistry classes this term, and I have been doing TONS of math all week in my homework assignments. Get
really familiar with your calculator!
Another thing, like somebody else said, whatever you do - do not get behind. Chemistry isn't a cram-it-all-into-one-weekend kind of class. You have to do the readings and the work as you go, because the concepts all build on each other and you have to be proficient at one thing before you can understand the next.
Plan on allowing lots of time outside of class. I'm taking two 5-credit hour classes with labs, for a total of 14 hours in-class time. I probably spent 18 hours outside of class this week, working on assignments, and it's just the first week of the term! Be prepared to spend a lot of time on this class in order to do well.