The ideal practice is to clean the oven most frequently because the longer you leave the oven dirty, the harder it gets to remove the tough grease and burnt-out food. Therefore, you should necessarily clean your oven every three months at least. Additionally, if you use the oven regularly, you can clean it once a month and ideally eliminate all food residue and stains. Thus, a clean oven is a sign of healthy and safe cooking, whereas a dirty one can lead to breeding germs and bugs, making your food unhealthy.