I have many students tell me that they are afraid to ask a stupid question in class. I tell them that there are NO stupid questions, only stupid mistakes because you didn't ask the question! Too many smart students in Calculus think that by asking a question they will appear weak. What most students don't know is that probably there are many other students with the same question in their head that they are afraid to ask! The look of relief on other students' faces when some else asks a question is amazing.
Another thing smart students have a problem with is writing down each step. Newsflash: by the time you get to Calculus you can no longer do the problems in your head. Calculus problems generally are difficult because it is not just a matter of memorizing a formula and applying it. In Calculus you are expected to extrapolate the knowledge you have learned to problems you have never seen before. This is scary for most students. However once you start to write down the given, write down the question, draw a picture and find a relationship between the two the problem is solved. You have to learn to be uncomfortable when you first read a problem and not immediately know what to do. Have confidence that you have learned all you need to know to do the problem and just start pulling the problem apart.
My best, best, best and most successful Calculus students are meticulous in writing down steps when solving a problem. And they are never afraid to ask a question!