Like others have said one of the easiest things to do is simply don't buy the junk.

Personally I found that the real game changer is finding a healthy snacking alternative. For me this is almonds and dried apricots. They're still quite a 'dense' energy snack but it scratches the sweet tooth itch and is much more filling. Plus you get the added protein, fats & micro nutrients that you would usually miss in processed items.

Try out some different alternatives (my wife loves to snack on dates and Greek yoghurt for example) and try mainly just to focus on finding something you enjoy so you can swap the habit.

Good luck!