Thank you for your question! The simple answer to this question is practice, practice, and practice. I will talk about the two classes separately as they are taught very differently. 
 
For physics 135, you will have online homework called “Mastering Physics”. Make sure that you know how to do every single homework question before you attempt the practice exams given (since there are only very few given). As long as you know how to do all the problems on Mastering Physics without assistance, attempt the practice exams. Since all of the questions are multiple-choice on the exam and the practice exam, make sure you actually know how to solve the problem (the formula used and approach). 
 
For chem 230, there will be a coursepack for every single exam (it is called PREP). There will be one PREP packet for each exam. Do the PREP questions as you are taking the exam. There is key for the PREP, so you can check yourself afterward. Start the PREP early and try to finish before the exam. If you know how to do every single question on the PREP, you are good to go for the exam. 
 
I hope my answer has been helpful. Good luck with the two classes! 
 
PMH  Haitong