What is the best way to cure and prevent mouth ulcers. i don't consume alcohol or tobacco.

Depends upon type of: There are many different types of mouth ulcers and each result from different causes. Prevention may or may not be possible. Treatment also depends upon what type of mouth ulcers you have. The best answer can be given by a dentist who observes your ulcers to see if they are the same or different over time. He\she can then discuss prevention and treatment with you.

Oral ulcers: If you are finding it difficult to properly treat these ulcers and your dentist is uncertain of the answer i would recommend finding a dentist that specializes or has advanced training in oral medicine. You can check with the american academy of oral medicine web site for a dentist in your area.