The first big thing is that they are expected to be well behaved while I slowly put their food bowl down. If there is a hint of growl or lunging, the food bowl comes back up again and only when they have restrained themselves does the bowl start to go down again - and slower than before. My dogs are seniors now, but they 'understand' that he who giveth the food can - and will - taketh the food if they give me any grief.
The second big thing is that they are expected to give up whatever is in their mouth on command. This requires ongoing training, and also started when they were wee-little pups. They understand that if I put my hand out palm-up, or grip what is in their mouth, and tell them to "release" they are going to loose whatever is in their mouth. If they give it up without a scene, then they get it back in a few moments. If they make a scene, or I have to pry it from their jaws, then they may not get it back. This has helped in situations when they managed to get something they shouldn't have (e.g., a dropped grape).