As people are saying, the "es" forms mean something permanent whereas "estar" is temporary. So "es" is used for things like cities, buildings, personality, etc. "Estar" is used for things like cleanliness, feelings, locations of objects, etc. This is probably a very silly trick, but I think of the lengths of the words to remember their meaning, so I would think "Es is short, the time I would take to figure out the thing is also short because it never changes. Estar is longer, and the time I would have to think about the thing is longer because it's changing and needs more thought." It's silly and it's a long way to remember something, but it's what I do.