I tried it myself, so I know it works and it's not hard at all.
First I said: I'm not buying drinks (soda, fruit juices...) in the store. I can drink water.
After some time: no more sweets. I made a list of sweets (chocolate, candies, chewing gum, cookies, cakes, ice cream...anything with sugar) and never bought any when I was in the store.
Then: no dairy (milk, yoghurt, cheese, butter, anything).
I left with potatoes, rice, pasta, bread, soups, vegetables and fruits and my body was not missing anything.
It can help if you make some kind of ideology from all this: "I do not eat sweets", until I... It is much easier than: "I may not eat sweets", since this is than a constant battle with temptations.