I had acne for the first 28 years of my life. I did two changes then: 1. Mostly ditch grains and unhealthy carbs; and 2. Drink a lot of water.
Since then, I don't develop acne. It started working immediately! But I don't know which one worked for me. In the weeks that I drink less water and/or consume some grains, I develop very small ones.
Hope this helps.