Practice good oral hygiene. Brush your teeth twice daily, and floss daily.
Use toothpaste without sodium laurel sulfate, which has been implicated in aggravating canker sores.
Avoid mouth trauma. Don't bite the insides of your cheek, and avoid exposing the lining of your mouth to sharp objects, including hard-bristled toothbrushes.
Avoid foods that are believed to trigger attacks. Chocolate, salted nuts and potato chips may contribute to canker sores, though there is currently little authoritative evidence of this.