I believe that what goes in, has to come out. Food will either be used by your body for energy, or your body will get rid of it through bowel movements. Toxins can also be excreted through your pores. So, make sure you are putting good stuff into your body.
For the most part I am pretty good about that. I eat lots of whole foods, I own a juicer and make celery, cucumber and carrot juice every morning, I snack on almonds or fruit. We don't keep junk in the house, but do occasionally buy cookies. Over all, I believe I eat an above average healthy diet.
But we do like McDonalds/A&W/Wendy's every now and then. Plus we have pizza about (or less than) once a week. Sometimes you just need what is convenient.
I haven't made any firm correlations to my diet and pimples. But as I mention I believe that what you eat comes out somehow. I am reducing the amount of toxins I ingest hoping that my body will excrete any junk I put in through the proper channels (liver, bowels) and not through my face.