It is essential that you have good bowel habits. A clean colon will reflect healthy skin. Constipation will allow toxins to build in the body. As skin is the largest organ in the body an unhealthy body will show on your skin.
Eat plenty of vegetables and fruit plus servings of meat, fish and chicken. Water and green tea are good for your whole body. Avoid bottled juices, soft drink, alcohol (especially the mixes) and coffee.
Regardless of what you may see about diet not being the cause of acne it is well recorded that bad fats and sugar contribute in a big way to poor skin. Of course excess weight will result from a fast food diet as well. MSM powder can help constipation as well as problem skin so give it a try.