micromass said:
Work hard, make lots of exercises, read several texts on the subject, make lots of exercises, watch khanacademy, make lots of exercises,...
In addition to what micromass has said:
Try to understand it at a deeper level, go into the chapter VERY slowly as to follow the steps of logic. Nothing should be swallowed.. you should make sure to chew down the information first.. to make sure WHY it works! That is the beauty of mathematics, because everything just makes SENSE! I think your problem is that you aren't spending enough time in calculus. But if you follow what I told you religiously then there should be no problem in spending the time in calculus because you will be interested.
Try to think of calculus aside from just studying history. Pretend your in this group of mathematicians and they are uncovering the beauty of mathematics right beneath your eyes. Think of the amazing insights they developed, and ask yourself: If I was in their shoes, how would I have tackled this problem? Pretend you are at the forefront of the world of mathematics trying to uncover the latest problem. Think of as many ways that the problem applies to our world. I hope this is making some sort of sense.
Know your mind, interest comes from within. You can spark the interest yourself. You are no longer at the whim of the sum of influences around you which accumulate over the period of your life. What makes you YOU is: = \sum influences
Humans have reached an intelligent level where they can influence themselves, simply by thought.
I took the time to write this out because not only is it important in any aspect of life, but because if you are interested in calculus itself it should be no problem mastering it!
Steps you can take to master calculus:
1) Take notes before the class, this can be very important; when you go to class, the material is being reinforced and you can come up with questions and look for loop holes in your understanding
2) Don't take mathematics at face-level. Take it apart, understand WHY! Heck, play with the mathematics if you so choose.
3) PRACTICE!