Create a pre-test that will test students on the most important areas of the subject you are teaching. The test should be a standardized objective exam that can be repeated at the end of the semester or school year. Questions should be basic and only test students on areas of common knowledge within your subject. Assess students at the beginning of the school year or semester. You need to know how much your students know about the subject you are teaching so that you can determine the effectiveness of your teaching by later comparing your initial assessment to a similar final assessment.
Analyze the results of the pre-test for the entire class and look for a pattern of particular questions that students seem to miss more than others. If the tests are multiple choice, you can determine whether or not students are all choosing the same wrong answer or if they are just missing the questions randomly.
Provide feedback to the whole class regarding the questions they missed. Discuss which questions were missed most frequently and why you believe this to be true based on the patterns you've seen. The goal in addressing the class is to teach them the art of error detection, or determining why they committed certain errors rather than choosing the right answer.
Instruct your students in the art of good test-taking. Show them how to read through questions carefully and eliminate the wrong answers while looking for the best possible answer. Discuss why some answers are better than others until your class is comfortable with the process. You may to do this several times throughout the school year.
Ask the students to provide their feedback on which questions were the hardest and why. Have them explain their train of thought on certain questions and why they chose the answers they did. By learning how to think like your students do, you can anticipate how they might respond on future questions of a similar nature and direct your teaching towards decreasing any possible deficiencies.