There are a lot of ways to go about this-- one of the most straightorward is try not to have a lot of snacks around. But I am sure that you know that this is frequently not possible. It is very frustrating to walk into a room where a half dozen people are munching away, and you have to remember not to snack.
One of my favorite tricks is to hydrate when I want to munch. Coffee, tea, diet soda, and seltzer flavored with syrups are all low in calories but are a good way to kill an urge to consume. Plus, when you are at an event you are still enjoying the buffet, just sipping a drink instead of filling a plate.
Another trick that I like, cheates a bit with the no snacking rule. I stretch out my lunch or dinner. That is, I save out some of what I normally would eat as part of a meal (fruit, chips, veggies) for a snack a bit later. You eat the same quantity of food as before (as long as you don't increase the size of your meals to make up for it) without the "eating between meals" issue.