Use your imagination and visualize yourself as a fit non-smoker when motivation starts to flag. Some people call this hypnosis but it is just using your imagination to help yourself.
As in so many behavioral issues, it is simply a matter of re-programming our mind. Giving up smoking is challenging, and self-hypnosis is a method that many are discovering as a simple way to help keep the mental attitude and motivation on course.
Rob Mellor has an excellent course on the subject you can read about it here. It is a series of recordings that you can listen to in the car or any other convenient place. Rob Mellor’s course is not free.