Mouth cancer, unfortunately, is on the increase. It kills more people than the more widely screened-for cervical cancer. Your dentist can screen you for mouth cancer and it would help them if you keep them informed about your smoking habits and alcohol consumption.
If you have an ulcer that doesn't heal up after 2 weeks, a red or white area in your mouth or a persistent swelling - bring it to your dentist's attention. It is probably nothing to worry about, but let your dentist see it. It is much better to be over cautious and your dentist won't mind. Sometimes the dentist won't be sure what the area is themselves and will refer you for a second opinion. Again, do not be concerned as it is just a precaution because the dentist might not have everything available in the practice to make a diagnosis with certainty.
How to reduce the risks? Stop smoking, drink less alcohol and eat healthily - 5 portions of fruit and vegetables a day.