If you can get close to eliminating sugar and simple starches from your daily diet, that alone will prevent a lot of plaque build-up and even slow/prevent advancement of tooth decay (within reason… Please see a dentist and get tooth decay fixed before it destroys your quality of life).

Sugary foods include things like dried fruit. Simple starches include crackers and most bread (I find a crusty open-crumb sourdough to cause less plaque buildup than a fluffy yeast loaf, despite being basically the same ingredients.)