Stopping tobacco consumption is way better than continuing it. For heavy smokers there is low dose ct scan but it's efficacy is still debatable. For tobacco chewers keep an eye for any white or red patches inside the mouth. Any ulcer in the mouth which doesn't heal within a week needs to be evaluated. If you find that its difficult to open your mouth (tightening) then also you need to see a doctor. Remember cancerous ulcers are painless to begin with !