A technique that (sort of) works for me, Darcey, is not one where I actually try to stop snacking altogether but where, instead, I set myself some tasks with, say, some biscuits and a cuppa as a reward at the end of it.
So, for example, I might feel like those biscuits, and the cuppa, right now but I'll tell myself that I'll have them as a reward for finishing the washing up, changing the duvet cover and clearing some of the rubbish from my desk. That prevents the process of eating from becoming a continuous one, thus cutting down a bit on the amount of junk food that I actually consume.