Read the school's evaluations carefully. Especially read the parts where the students can interject some true input. If a student says that there could be more slides or PowerPoint presentations, address that the next semester and see if this is removed from the comments. If a student says a course is boring, check it against their other answers.
Ask the students at the end of the semester what they thought. If you are a good instructor that has earned the students trust, they will be honest with you. They will feel that it will not affect their grade and may help them if they take another course with you. The main thing is to be honest with them because they will be very honest with you.
Pass out your own evaluation at the end of the semester. There are usually questions that are not on the school's version of the evaluation that you want to know. This is the best way. Have an assistant pick them up and then give them to you after final grades are posted. It is best to have this approved by your department chair. Some good questions to include are: Were the assignments clearly defined? Was the course moving too fast or too slow? Were the review sheets helpful? Was the instructor available outside of office hours?"
Perform a self-evaluation. Examine your self-developed evaluations first. You can use a Scantron sheet and the results can then be plotted out for easier use. If there is a low score in some area, find a way to address it. Examine the audience, your students and their demeanor. A lot of information can be derived from body language. For example, you may notice students burning out because of the writing assignments. If so, re-evaluate your writing assignments and alter them effectively. Remove one or shorten the required length. Ask yourself if you keep their attention. The best way to tell is if you are teaching is improved grades throughout the semester. According to "Effective Teaching Methods," if grades climb from 75 to high 80s over the semester, you are effectively teaching.