Here's an example.  I once gave a woman who wanted to stop biting her fingernails a post-hypnotic suggestion that whenever she would move her hands toward her mouth, she would immediately become aware that she was about to bite her nails.  I suggested to her that she would stop immediately because of her powerful desire to grow long, beautiful nails that everyone would notice and compliment her on.  The trigger for this post-hypnotic suggestion was the movement of her hand(s) toward her mouth.  It worked like a charm because of the woman's powerful desire to have long, beautiful nails that everyone would admire.  She quit after the first session.

More hypnosis techniques:

Eye Catalepsy

Eye Fixation

Staircase Technique

Metaphors

Fractional Relaxation

Conversational Hypnosis

Indirect Suggestions

Double Bind

Guided Imagery

Visualization

Post-Hypnotic Suggestions

Direct Suggestions

Confusion Technique

Tongue Relaxation