Negative Suggestions are not not good
I was talking to a student recently who was going through her hypnosis training. She was very concerned about not saying 'not'. I told her to relax and just speak normally to clients. There is a huge amount of nonsense talked about not using negative suggestions in hypnosis.
I don't think it matters if you use negative suggestions or not. Some trainers tell their students that if they tell the client to 'stop smoking' all the mind does is to hear the word 'smoking' and not the word 'stop' and it puts the idea of smoking into the client's mind.
Do not think of an elephant
The evidence for this is always the NLP example: 'Do not think of an elephant'. The point is that of course the image of an elephant comes to mind. NLP teaches that the mind does not notice the word 'Not' and only acts on the thing that comes after the 'not'. The theory is that a negative suggestion emphasizes the thing mentioned.
But if that was true, then the word 'not' would apply to 'think' rather than 'elephant'. If the 'not' was operating as NLP theory says, you would stop thinking. Of course that doesn't happen. The sentence 'Do not think of an elephant' gets parsed as a whole unit.
Even as it being said, the language processing part of your brain is trying to make sense of the whole unit of speech. In fact while the stream of words is being heard, processing is continuously redefining the sense of the sentence. Think of the times when you have only realized what somebody said long after they had said it.
The sentence is evaluated as a unit. That is why you get confused by long rambling sentences. After the sentence has been evaluated, the core idea of the sentence is what remains. The actually words are largely ignored. The 'elephant' comes to mind because your mind is waiting to hear what comes next about that elephant. The image of the elephant stays in your mind because your mind is waiting to hear if you are going to feed it or shoot it.
Do not think of an elephant is oversimplified
The NLP view on negative suggestions is very simplistic. It does not reflect how the mind actually processes words. A moment's thought will show that if that was true, all hypnotherapists would be out of business. Because all you would have to say is something like 'Don't lose weight' and the client would give up overeating, or say 'Do not eat healthy' and the obesity epidemic would be over. Or how about 'Don't stop smoking' to have all the world give up smoking instantly?
The whole negative suggestions theory about 'Never say Not' is overdone in my opinion.