To become a good listener, you must learn two things: the first time you listen to the text, VISUALIZE the most you can; when you start writing, NEVER leave a GAP: write down between slashes what the words SOUND like. In this way, when you revise your text, you have a chance of imagining what the word could be. In any case, if you write down the sounds at least, the teacher can help you monitor if your listening skills are improving. It could also be useful in exams, because if you write the sound at least (between slashes, and using all the phonetic symbols you can use), the spelling could be wrong but the teacher would be able to see you knew which the word was.
Method - How I dictate in class and what you should do
I read the whole text first - You visualize
I read each chunk of speech twice - Don't ask me to repeat, I will read it twice. Try not to leave gaps.
I read the whole text again - You check it all (fill in any gaps or best, check spelling)
After the dictation has been checked, you should record in your List of Mistakes and Errors whatever was wrong. Use this list after you check your next dictation and try to analyze your progress.
Read about a method for Self-dictations here. Use the audios at this website to practice, or the CD-Rom I recorded for you, and your own audio material.