It helps to have someone watch you and tell you if you are doing what you think you are doing. A week ago my wife recorded a video of my swimming and I realized that my legs were much busier than I thought and my arms speared shallower than I thought (and my left arm also not as wide as I thought). So, for the last few days, I've been focusing on quieting my legs and spearing deeper and wider, occasionally asking my wife to watch for those things and give me immediate feedback. I was amazed at the decrease in my SPL in just one week.
Besides the value of feedback, the other lesson I drew from this is that, for every problem in the front, there is likely an associated problem in the back (and vice versa). So I second swimust's suggestion - make sure you get feedback on both your front and back work.