Using a sneeze or saying ‘excuse me a minute would break someone’s flow and induce amnesia (a pattern interrupt). If you follow this up with either continuing to imply forgetting, or you could talk about subjects that lay down the pattern for forgetfulness. Like having a name on the tip of your tongue etc... Another way is while they are in this state of having forgotten go back to an earlier conversation, this sandwiches the now forgotten bit.
So for example; if you were talking about the weather, then talking about something you later want the person to forget, you can interrupt them then once interrupted go back to talking about the weather so that it is as if none of the rest of the conversation happened.
There is a brief example of inducing amnesia at the beginning of this video
http://uk.youtube.com/watch?v=cOkqIEiYYtM
Recently an idea came to me to induce amnesia. It appeared to be effective. I gave an example of how a child can be eating all of their sweets, engrossed in that and then they reach the end of the pack of sweets and they look up to the parent and hold out the bag and say 'It's.....' (I never finished the sentence).
I expected the unconscious to know all likely endings to that sentence in that situation. What I wanted was to narrow down to just one likely meaning (It's all gone). I planned on doing this by saying something else with the same messages so that the unconscious can pick up on what is similar about both messages.
Next I said 'You know that the roman numeral for 4 is iv, and you know how you can see something and read it in different ways and with different meanings, and you know what it would look like to see the Roman Numeral for 4 in front of you with the number 4 next to it, with the number 10 at the end and the word 'got' just before that...' (iv 4 got 10)
The unconscious did appear to pick up on these together from the response I got...
Other ways are using distraction, or changing subject. In childcare I used to do this a lot, a young person would be beating someone up and I would say I thought I heard someone at the door. They would immediately stop and go and check, by the time they got there I would be already talking with them about something else to keep them active and get their train of thought as far from where it was as possible.
I used to practice doing distraction indirectly, like looking at something, or at them (like their nose) until they want to know what I am looking at. Especially with looking over somewhere people often lose their train of thought and look, before they realise why they are looking. Or you can sneeze or something that will equally stop them, or just say 'excuse me a minute' any interruption often works brilliantly especially when you follow it up with implication that they have forgotten.
In hypnosis I like to guide people into experiences (like along a beach for example) then have them settle down and drift off into a daydream (about walking in the woods for example) then find somewhere else to rest (like sitting under a tree) and drift off again (like looking up at clouds and wondering what it would be like to be on another world looking up at clouds on that world) then I do the work with them and sandwich it by reversing the process so that what is in the middle becomes the most difficult to remember.
I think one of the best ways to create amnesia is not to ask about the experience (like not asking about a dream someone has just had when they wake up). If they don't get asked and then go home and maybe later on that day or the next day they get asked they often don't seem to remember (or not much if they do), almost like if you waited a day to ask someone about a dream they had, they probably wouldn't recall much of it.