What’s the best way to keep the kitchen sink drain clog-free?

First, dump a half-cup of baking soda into the drain. Pour a quarter-cup of vinegar into that. Cover the drain and let it sit for 15 minutes; the mixture will foam. Then flush the drain with cold water. 

Do this periodically to keep your drain flowing freely. 

Avoid using chemical drain cleaners, especially if your home’s plumbing is old.