I always mix up my integration and differentiation. How do i stop this?

First thing to do is practice. Practice makes perfect. You are not going to get through your differentiation and integration by doing only a couple of questions on these topics. You need to take one topic at a time and do a ton of questions on it. Normally, you would be provided with questions in your textbook at the end of every topic. Make sure you do every question and take note of the ones you cannot solve. For example, assign one week to questions on differentiation and the next week to integration. During your third week, try doing questions on both in one sitting to test your knowledge. The trick is a lot of practice.