What are the best tips to prevent mouth ulcers/canker sores?

None: There is no way to prevent them. Many people experience them with illness or stress. Avoid these two things and you might have fewer.

Pattern?: Canker sores usually are triggered by something that you do. Keep track of what common things that you eat or do just before the canker sore appears. The trigger can activate a virus that displays itself as the canker sore.